Milk thistle is a powerful and safe herb for liver support. Its extract (silymarin) boosts detox, lowers inflammation, and increases antioxidant defense, which is beneficial for liver and gallbladder issues, diabetes, and autoimmune diseases. Read on to learn more, along with dosage information and smart ways to improve the poor bioavailability of its active compound silybin.
Milk Thistle Snapshot
- Great for improving liver function and detoxification
- Has gentle action and a diverse array of beneficial effects
- Good antioxidant and anti-inflammatory
- Improves metabolism and lowers lipids
- May fight cancer and reduce radiation side effects
- Low risk for side effects
- There are stronger anti-inflammatories and antioxidants out there
- Regular extracts and supplements have poor bioavailability
- Milk thistle tinctures taste slightly bitter
What is Milk Thistle (Silymarin)?
Milk thistle (Silybum marianum) is a medicinal plant that belongs to a large family of flowering plants (Asteraceae). It has been used traditionally for thousands of years as a “liver elixir” for a variety of diseases to do with liver dysfunction or gallbladder problems. It was also used to protect the liver against snake poison, insect stings, mushroom poisoning, and alcohol abuse [1, 2, 3].
Milk thistle is a relative of dandelion and regular artichoke. Sometimes it’s called “wild artichoke”. It’s native to Southern Europe, Russia, Asia, and Africa and is now also cultivated throughout the world. The seed-like fruits of the plant are used medicinally. Traditionally, though, the leaves were used in salads and the fruit of the flower roasted as a coffee substitute [1, 2, 4].
Silymarin is a mix of active components that are highly concentrated in a standardized extract of milk thistle seeds .
In the US, milk thistle is among the most popular herbal supplements. It’s also commonly used in other parts of the world, especially in Germany – the largest producer of milk thistle (Madaus). The German Scientific Board recommends its use for indigestion, toxin-induced liver damage, cirrhosis, and liver inflammation [5, 6, 7].
Although more studies are needed, milk thistle is a great example of traditional plant knowledge being successfully put to scientific scrutiny. Since the 1970s, milk thistle extracts and its main active component (silybin) have been regarded as an official medicine for liver diseases .
Numerous high-quality clinical trials have investigated the health benefits of milk thistle in the 21st century; over 70 human studies in total have been published so far. This article will take you through all the latest scientific findings and their health implications.
Bioactive Components (Silybin)
The seed-like milk thistle fruit (achenes) contains the active ingredient silymarin along with other compounds such as:
- Other flavonoids (taxifolin, quercetin, kaempferol, apigenin, naringin)
- Oils (linoleic, oleic acid, and palmitic acid)
- Vitamin E (Tocopherol)
- Plant sterols (campesterol, stigmasterol, and sitosterol)
- Some sugars and proteins
Silymarin makes up to 3% of the dry fruit, while fruit extracts can have up to 80% .
Silymarin is a complex mixture of flavonoid complexes that includes :
- The flavonoid Silybin (a flavonolignan), the most active ingredient
- Other Silybin-like flavonoid complexes (Silybins and isosilybins A and B)
Silybin concentrations in various extracts can vary:
- The highest concentration of silybin in extracts is 50 – 70%
- Silybin concentrations in common supplements are 20 – 40%
Tip: Don’t get confused when you look at the supplement label. Remember: Milk thistle extracts should be high in silymarin (60 – 80%) and a large part of this silymarin complex should be silybin (at least 20% but aim for those with 50 – 70%)!
Mechanism of Action & Metabolism
Silymarin acts on many important pathways in the body to :
- Increase liver regeneration by enhancing the production of DNA and RNA
- Prevent poisoning from drugs and toxic substances by making the membrane of liver cells less penetrable to them
- Stop liver viruses such as Hepatitis C from multiplying
- Neutralize free radicals and increase levels of the master antioxidant glutathione
- Reduce inflammatory cytokines (TNF-a, INF-b) while increasing anti-inflammatory defense (IL-10)
- Stop tumor growth and kill cancer cells by triggering their death pathways (p53) and turning on cancer-fighting genes
However, silymarin has poor bioavailability (check the dosage section for ways to overcome this). Plus, absorbed silymarin is broken down and transformed into inactive metabolites in the liver. Most of it is eliminated through bile, together with bile acids .
The legend about the “blessed virgin thistle”
The fruits of milk thistle, not to be confused with blessed thistle (Cnicus benedictus), have long been used by mothers for stimulating milk production. Its use was associated with a legend according to which the white veins of the plant’s leaves were a drop of the milk of the mother of Jesus who found shelter in a bower of the plants. Thanks to this legend, the plant is sometimes called Mary thistle, holy thistle, blessed virgin thistle or Christ’s crown .
The Health Benefits of Milk Thistle
1) Milk Thistle Protects Liver
Out of all the health benefits listed here, milk thistle has been most researched for its powerful liver-protective action. A large recent analysis of 17 clinical trials concluded that silymarin can reduce liver enzymes ALT and AST, common markers of liver damage .
Fatty Liver Disease
A combination of Milk thistle’s active compound, Silybin, phosphatidylcholine, and vitamin E over 1 year improved non-alcoholic fatty liver disease (NAFLD) in a clinical trial of 179 people. It reduced liver enzymes, insulin resistance, and liver scarring with no serious side effects. Some of the included Hepatitis C+ participants included in the trial experienced the same benefits [11, 12].
However, the active ingredients can reach higher blood levels in people just with fatty liver disease than in those with Hepatitis C. After being absorbed, silybin is secreted into the gut with bile. People with Hepatitis C can’t absorb silybin again and “recycle” it, which lowers its blood concentration .
Overall, silybin from milk thistle improves fatty liver disease, even in people who also have Hepatitis C. But those with Hepatitis C may need higher doses (2.1g/day of silybin) to compensate for the liver damage that affects bioavailability .
Hepatitis C and B
An analysis of over 1k people concluded that people with hepatitis B or C who took milk thistle are less likely to die of liver-related issues .
In an observational study of over 1,000 people with hepatitis C, those with the more severe forms of the disease who used silymarin were less likely to experience worsening and further liver damage (cirrhosis) .
In one clinical trial of 36 people with hepatitis C who didn’t respond just to drugs (Peg interferon + ribavirin), IV silybin alone or as an add-on to the anti-Hep C drugs greatly reduced viral activity and load. In 7 people, the virus became completely undetectable after 6 weeks (15 – 20 mg/kg) .
However, in another trial of 154 people with Hepatitis C who previously didn’t respond to standard therapy (interferons), oral silymarin (2.1g/day) did not lower liver enzymes or virus activity much after 6 months. But the researchers didn’t measure the silybin content in the extract, blood levels of its active components, nor focus on the virus load [18, 19].
According to an analysis of almost 400 people, oral silymarin has modest effects on reducing the activity of the Hepatitis C virus, not much different from the placebo. Silybin, the active ingredient, may work better if given through a high-dose IV in people with Hepatitis C, but further studies are needed .
People with liver disease often have very high ferritin levels due to liver inflammation and injury. In a trial of 37 people with Hepatitis C, silybin combined with phosphatidylcholine reduced ferritin levels in ~80% of the cases over 12 weeks [21, 22].
People with any Hepatitis virus can experience a sudden, acute worsening and liver inflammation. In a clinical trial of 105 people such cases, silymarin (420 mg/day) reduced symptoms, improved jaundice and bile flow over 4 weeks .
Hepatitis and HIV (cellular studies)
Milk thistle was active against Hepatitis C in many cellular studies. Silymarin blocks the Hepatitis C virus from entering cells, infecting them, and dividing. But in this cellular study, it wasn’t active against all strains of the virus, so some people may not respond to it [1, 24].
In one cellular study, silybin protected from the HIV virus, reducing its activity and division. It also reduced immune activation and inflammation that contributes to the spreading of HIV .
Alcoholic Liver Disease
Silymarin (450 mg/day) increased the master antioxidant glutathione and reduced oxidative stress in red blood cells in a clinical trial of 60 people with alcoholic liver disease after 6 months. It didn’t affect liver function or enzymes in this study, though .
Protecting the Liver from Drugs and Toxins
Milk thistle may protect the liver from drugs and toxins .
In animals, silymarin and silybin protected the liver against damage from alcohol, toxins (carbon tetrachloride and thallium), chemotherapy drugs (cisplatin), Tylenol (acetaminophen), radiation, iron overload, and the poisonous mushroom death cap (Amanita phalloides) [2+, 29].
In a clinical trial of 50 children with leukemia, milk thistle protected the liver and reduced damage from chemotherapy drugs after 1 month .
In a woman with leukemia, silymarin (800 mg/day) reduced the side effects of chemotherapy drugs and protected the liver over 4 months .
Milk thistle doesn’t protect the liver from all drugs. For example, it didn’t protect the liver from anti-tuberculosis drugs in a study of 380 people. On the contrary, it even slightly increased the risk of liver damage .
Most mushroom poisonings worldwide are from a mushroom called “death cap”. Milk thistle is the number 1 antidote for death cap poisoning, given as IV silybin (oral silybin doesn’t work). It saved lives in over 90% of 1,500 cases in the US, which is better than any other antidote. It should be given within 48h to prevented severe liver damage and increase survival [33, 34, 33].
Quality of Life
In a survey of 32 people who received liver transplants, those who used milk thistle and other herbal products had better problem-solving skills, considered the supplement investment worthwhile, and reported better overall health .
This does not speak to the benefits of milk thistle, but shows that people who tend to take their health into their own hands actively seek natural alternatives.
2) Milk Thistle Liver Detox from Chemicals and Toxins
The liver breaks down and helps eliminate all harmful substances, both from waste products produced in the body and those that enter via food and environment. Since milk thistle protects the liver, many people use it to facilitate detox and reduce disease risk.
Milk thistle reduces oxidative damage and inflammation and helps regenerate liver cells. It boosts glutathione, the liver’s key antioxidant, as well as the protective enzyme SOD. It may help detox the liver from pollutants, environmental toxins, and drugs in healthy people based on the mentioned clinical studies [36, 37, 38].
The exact effects of milk thistle on healthy people who want to detox hasn’t been confirmed. But short occasional detoxes may be helpful even in people not exposed to any specific toxins. In one study of 25 healthy people, a 7-day detox improved wellbeing and liver health. Milk thistle is a safe supplement and could be used in short detox protocols, alone in combination products [43, 44].
3) Milk Thistle is an Antioxidant
In a clinical trial of 40 people with type 2 diabetes, Silymarin (420 mg/day) over 45 days enhanced antioxidant defense, boosting total antioxidant capacity and key enzymes such as glutathione and SOD. It also reduced the inflammatory marker CRP .
According to cellular studies, milk thistle acts as an antioxidant by:
- Activating the body’s detox hub, Nrf2 .
- Blocking the master inflammation pathway called NF-kB .
- Increasing mitochondrial health and activating Heat Shock Proteins, which protect cells and tissues under stress [R, R].
- Increasing sirtuins, which help conserve energy, reduce aging and inflammation .
- Neutralizing free radicals, chelating free iron and copper .
- Blocking harmful enzymes that increase oxidative stress .
4) Milk Thistle Reduces Inflammation
Tightly tied to its antioxidant activity, milk thistle is a strong anti-inflammatory. It blocks most pathways that trigger or worsen inflammation in the body.
In pregnant mice with infections, its active compound silybin reduced inflammation in the brain and preterm births. It lowered inflammatory substances (IL-6, IL-8, PGE2) and enzymes (COX-2) and gene expression (MMP9) .
5) Milk Thistle May Reduce Autoimmunity
One of the reasons why women are more susceptible to Th17-dominant autoimmune diseases is because estrogen is involved in maintaining a healthy immune response. In order to reduce the Th17 inflammatory response, estrogen receptors need to be activated. Estrogen normally does this, but its levels drastically fall in women after menopause .
Milk thistle can activate estrogen receptors and reduce autoimmunity. In a study of healthy people and those with rheumatoid arthritis, silybin had a beneficial epigenetic effect (increasing ER-beta and miR-155). It binds to estrogen receptors in white blood cells, reduces the autoimmune response and inflammatory cytokines (IL-17 and TNF-a) .
6) Milk Thistle for Infections
It was also active against hard-to-treat bacteria, the so-called Methicillin-Resistant Staphylococcus Aureus, in cells .
Milk thistle may also help fight parasites. Silymarin reduced a parasitic infection from blood-flukes (Schistosomiasis) in the liver and killed the parasite eggs in mice .
7) Milk Thistle Protects the Brain
Silybin reduced brain injuries and brain inflammation in mice with infections .
It prevented memory loss and improved learning in rats by reducing oxidative stress in the brain. This active compound from milk thistle reduced damage in the brain’s memory hub, the hippocampus. The hippocampus is part of the limbic system, which controls emotions and the stress response. This region is often inflamed in people with brain fog .
It also had a beneficial epigenetic effect in mouse brains. Silybin increased the expression of BDNF, which helps make new brain cells, and of tyrosine receptor kinase B (TrkB), which helps make and strengthen new connections in the brain in response to BDNF .
Silymarin reduced symptoms of Parkinson’s disease and damage from stroke in mice. It neutralizes free radicals in the brain, blocks the master inflammation pathway NF-kB, and reduces damage to brain cells. It lowers the activation of the brain’s immune cells (microglia), which may help prevent many neurodegenerative diseases [57, 58].
8) Milk Thistle May Improve OCD
As milk thistle protects the brain, it may also help with mental health disorders. In one clinical trial of 35 people with OCD, milk thistle extract (600 mg/day) worked as well as the standard SSRI drug (fluoxetine) to reduce OCD symptoms over 8 weeks .
9) Milk Thistle May Help with Diabetes
Milk thistle can be combined with berberine for blood sugar control. In one study of 85 people with type 1 diabetes, this combination reduced the insulin doses needed to keep blood sugars in check and also lowered blood fats .
In a trial of 60 people with diabetes and alcoholic liver damage, Silymarin (600 mg/day) improved insulin resistance and oxidative stress while reducing the need for insulin injections over 1 year .
10) Milk Thistle Improves Metabolic Syndrome
Milk thistle is a promising natural alternative for people with metabolic syndrome .
In 136 obese people with type 2 diabetes, a combination of berberine and silymarin improved all harmful disease markers after 6 months. It reduced fasting blood glucose and insulin, improved insulin resistance, raised HDL, reduced total, LDL cholesterol, and triglycerides. It also reduced BMI, waist circumference, and belly fat .
In 51 people with type 2 diabetes, silymarin (600 mg/day) didn’t only reduce blood sugars but also lowered total cholesterol, LDL, triglycerides, and liver enzymes (AST and ALT) .
In another study of 40 people with type 2 diabetes, Silymarin (420 mg/day) improved insulin resistance, blood triglycerides, and increased the beneficial HDL cholesterol over 45 days. Plus, it reduced the inflammatory marker CRP and increased antioxidants [61, 62].
In 137 people who didn’t tolerate high doses of lipid-lowering statin drugs, silymarin with berberine (~200/1200 mg/day silymarin/berberine) improved blood sugar, insulin, and didn’t worsen blood fats when the drugs were stopped .
In cells, milk thistle can block Pancreatic Lipase, an enzyme that breaks down fats in the gut and helps absorb them. By blocking this enzyme, milk thistle may reduce the amount of fat absorbed from the diet .
11) Milk Thistle Protects the Heart
One way that milk thistle can protect the heart is indirectly, by lowering blood fats that contribute to hardening of the arteries and heart disease. Milk thistle reduced triglycerides, total and LDL cholesterol and increased HDL cholesterol in several clinical trials [61, 62, 67].
But it may also lower blood pressure by reducing inflammation. In one study, silymarin was applied to the immune cells of pregnant women with high blood pressure. It blocked all the major inflammatory pathways (TNF-a, IL-1b, NF-κB) .
Milk thistle prevented heart injury and disease in rats. It also protected muscle cells from injury by restoring healthy activity in the mitochondria. Plus, milk thistle can turn on genes that reduce inflammation and protect the cells from damage (Bcl-2) [71, 72].
12) Milk Thistle May Fight Cancer
In one clinical trial, 60 people with benign polyps in the colon (which often develop into colon cancer) took a herbal blend with milk thistle, a flaxseed antioxidant, and oat fiber for 2 months before colonoscopy. The combination increased estrogen receptors in the colon, which helps kill these “pre-cancerous” cells and prevent colon cancer .
Milk thistle has low bioavailability, but standardized extracts can still reach the blood and cancer tissues. In 12 women with breast cancer, a combination of silybin and phosphatidylcholine (2.8 g/day) for 4 weeks before surgery was safe and built up in the breast cancer tissue more than in healthy tissue .
In one study, even high doses (up to 13 g/day) of a special milk thistle formulation (Silybin-phytosome) over 4 weeks was safe in 13 people with prostate cancer .
Milk thistle could also be added to sunscreen to naturally protect against skin cancer, as it prevented skin damage in animal studies .
- Increasing cancer cell suicide (apoptosis)
- Preventing cancer cells from spreading and invading other tissues
- Stopping cancers from making blood vessels that help them survive
- Blocking the abnormal division of prostate, ovarian, breast, lung, skin, bone, and bladder cancer cells
- Reducing the expression of inflammatory genes
13) Milk Thistle May Reduce Chemo and Radiotherapy Side Effects
Silymarin gel 1% applied on the palms and soles of hands and feet protected from skin damage typically caused by a chemotherapy drug (capecitabine) in 40 people with stomach cancer .
In 77 people with cancer undergoing radiotherapy of the head and neck, silybin (420 mg/day) reduced painful mouth inflammation over 6 weeks .
However, milk thistle didn’t reduce kidney damage from the chemotherapy drug Cisplatin in one small clinical trial .
In mice with lung cancer, milk thistle reduced lung damage from radiation and improved survival .
14) Milk Thistle Improves Bone Health
Milk thistle (silymarin) improved bone healing and increased bone mineral density in mice with bone fractures .
Milk thistle may compensate for low estrogen levels after menopause, as the drop in estrogens increases the risk of osteoporosis. It prevented bone loss and increased the activity of cells that help mineralize and rebuild bones in postmenopausal mice .
In bone cells, milk thistle boosted the activity of bone-forming cells and blocked bone-degrading cells .
15) Milk Thistle Estrogen Effects
Milk thistle has estrogenic effects, which can be a double-edged sword.
But it can thicken the uterus lining and increase its weight. This can be harmful as it increases the risk of uterine cancer .
Milk thistle alone doesn’t affect menopausal symptoms. But it may work in combination with other supplements, mentioned in the synergies section.
16) Milk Thistle May Increase Milk Production
Milk thistle has been used traditionally by pregnant women to increase milk production. Clinical trials are lacking to support this, although milk thistle is probably not dangerous if used by pregnant women [91, 92].
17) Milk Thistle Reduces Iron Overload
The active compounds in milk thistle act as iron chelators, which can be useful for binding excessive iron in genetic disorders of iron buildup.
Silybin reduced iron absorption in 10 people with a genetic disorder that causes iron buildup and overload (Hemochromatosis) .
According to a large review 74 studies, silybin from milk thistle reduces high iron and organ damage in people with thalassemia when used as an add-on .
18) Milk Thistle May Protect Red Blood Cells
Free radicals can damage red blood cells, especially in people with genetic disorders that affect them (such as sickle cell anemia and β-thalassemia). Silymarin neutralized free radicals in red blood cells, increased their glutathione levels, and reduced their breakdown .
19) Milk Thistle May Help with Weight Loss
Silybin blocked fat cells from developing and dividing in test tubes .
In human fat tissue, it reduced fat storage and the size of fat cells. It could also turn on fat-burning genes, such as SIRT1, PPAR alpha, and Pgc-1alpha, which could potentially help with weight loss .
It’s uncertain if milk thistle can aid in weight loss in humans, though.
20) Milk Thistle Improves Acne
In a trial of 14 people, a combination of silymarin (210 mg/day), N-acetylcysteine, and Selenium reduced acne after 8 weeks by 53% .
Some studies in cancer patients showed that creams or gels with milk thistle protect the skin, reduce inflammation, and prevent damage. Skin products with milk thistle may help with acne and skin irritation too but haven’t been tested yet.
21) Milk Thistle May Improve Bile Flow
Based on animal and cellular studies, milk thistle may improve bile flow and help with diseases in which the flow is blocked. Often, liver disease is the cause, but it can also be due to a bile disorder. Milk thistle increases the production of bile salts and their secretion into the gut [101, 102].
22) Milk Thistle for Heartburn
The European monograph mentions heartburn and indigestion as one of the uses of milk thistle.
The popular heartburn product Iberogast contains milk thistle along with 8 other herbs. Iberogast improved indigestion, stomach pain, and heartburn in 3 studies. It has been around for 40 years and has a good safety profile [103, 104].
Milk thistle is a mild bitter. Bitter herbs reduce indigestion by increasing the secretion of stomach acids and digestive enzymes, as well as by activating the vagus nerve. As a mild bitter, milk thistle may reduce heartburn on its own, but studies are lacking to support it .
23) Milk Thistle for Hangovers
Due to its liver-protective effects, some people use milk thistle to reduce hangovers. Clinical studies have not investigated this (and expectedly so), but some animal studies may actually back it up.
In mice given a lot of alcohol over a short period of time, milk thistle protected the liver from injury. It also reduced inflammation and boosted antioxidants .
24) Milk Thistle and Anti-Seizure Drugs
SIlymarin reduced liver injury from anti-seizure drugs in 55 children with epilepsy .
It also increased the effects of anti-seizure drugs in rats. Milk thistle blocks Pgp, a protein that stops drugs from being absorbed in the gut or from passing to the brain. This way, it increases the amount of anti-seizure drugs that can reach the brain [108, 109].
25) Milk Thistle May Protect the Kidneys
In one clinical trial, silymarin (210 mg/day) for 8 weeks in people on dialysis reduced inflammatory cytokines, especially TNF-alpha .
It also protected the kidneys in animal studies and boosted antioxidants in kidney cell studies .
26) Milk Thistle May Help Heal Wounds
Silymarin increases skin regeneration and decreases inflammation in rats with wounds. Silybin sped up wound healing in rats by turning on genes that help the skin rejuvenate. In cellular studies, milk thistle gel increased collagen and the activity of collagen-producing cells (fibroblasts) .
27) Milk Thistle May Increase Fertility
Since milk thistle also has estrogen-like effects, its benefits for increasing fertility in men would need to be studied well in humans. Although men need healthy levels of estrogen to maintain fertility and sexual health, phytoestrogens that over-activate estrogen receptors usually reduce libido in men and increase the risk of erectile dysfunction .
Milk thistle could potentially be used to increase the chances of successful In vitro fertilization, but more studies are needed .
28) Milk Thistle and Prostate Health
A mix of silymarin and selenium reduced prostate symptoms in a clinical trial of 55 men. It improved urine flow and reduced bladder fullness .
The same combination reduced blood fats that are linked to prostate cancer worsening in men who previously underwent prostate-removal surgery .
29) Milk Thistle for Premenstrual Syndrome (PMS)
Women who experience mood changes, bloating, cramps, and breast tenderness in the premenstrual phase are more likely to have high CRP, a marker of inflammation. No studies have examined the effects of milk thistle on premenstrual syndrome. But since it did reduce CRP in some studies and is a safe supplement, it’s possible that it could help with PMS [62, 116].
Milk Thistle Synergies
- The combination with berberine improves metabolic syndrome and type 1 diabetes [67, 64].
- Berberine and Milk thistle added on to statins improved blood lipid levels .
- Silybin with Vitamin E and Phospholipids work together to reduce chronic liver damage .
- Milk thistle increases antioxidant defense in combination with Bacopa monnieri, Ashwagandha, N-acetyl cysteine, Curcumin (turmeric extract), green tea extract, gotu-kola powder, Ginkgo biloba leaf extract, Aloe vera powder .
- A combination with garlic, Aloe vera, black cumin, Plantago psyllium, and fenugreek was used for advanced type 2 diabetes .
- Milk thistle with red yeast rice extract and octacosanol improved blood fats and inflammation .
- Milk thistle was combined with selenium to improve prostate health [114, 115].
- To reduce menopausal symptoms, milk thistle was combined with black cohosh, dong quai, red clover, American ginseng, and chaste-tree berry .
- In Iberogast for indigestion, milk thistle is combined with bitter candytuft, chamomile flower, peppermint leaves, caraway fruit, licorice root, lemon balm leaves, angelica root, and celandine herbs .
Milk Thistle Dosage & Forms of Supplementation
Milk thistle is considered a very safe herbal supplement. Standardized milk thistle extracts should contain 70 – 80% Silymarin. Ideally, the silybin content should also be mentioned and account for ~40% (the higher the better).
- The typical silymarin dosage used in most studies was ~420 mg/day divided into 2 or 3 doses.
- In people with liver disease, the typical dosage is higher, around 1.3 g/day of the standardized for 6 – 8 weeks (divided into 3 doses during the day). For maintenance, the dose can be reduced to 280 mg/day .
- Silymarin doses up to 2.1 g per day may need to be used in people with viral hepatitis, especially in those with a chronic hepatitis C infection. Even so, IV silybin may work better than oral extracts in people with serious liver damage .
- Very high doses of the silybin IV solution are used for mushroom poisoning.
Milk thistle appears to be safe even if used daily for over 3 years. In cancer patients, the highest safe dose was about 13 g/day .
Milk thistle is available in many forms as a supplement. Milk thistle supplements, including silymarin extracts, include all the following:
- Intravenous solutions
Milk thistle has a bitter taste, which you will notice if you take it as a tincture. This helps if you’re taking it for indigestion but can be unpleasant otherwise.
Some people consider that taking organic milk thistle has additional benefits. Organically-grown plants sometimes have higher concentrations of bioactive compounds, but this has not been confirmed for milk thistle. It’s more important to make sure the supplement you decide to buy is standardized to the active ingredients.
What’s the best time to take milk thistle?
Daily milk thistle doses are usually divided into 3, which can be spread out evenly during the day. Milk thistle has poor bioavailability, though (more about this below), but taking it with some oils or fats is one way to increase its absorption.
Bioavailability Issues & Ways to Overcome Them
Silybin, the main active component in the standardized milk thistle extract Silymarin, has poor bioavailability. Only around 20 – 50% of it gets absorbed from the gut. This is because silybin can’t dissolve in water that makes most of the stomach and gut fluids. What’s even worse is that stomach acid can also degrade it, so sometimes it won’t even reach the gut.
There are many ways to overcome its bioavailability issues. Some smart approaches have been researched and several of them can be easily applied while others are commercially available, such as :
- Berberine increases the bioavailability of silybin and the two act together in synergy 
- Other flavonoids (such as quercetin) increase its absorption 
- Fats, proteins, amino acids, and cholesterol increase its absorption 
- Vitamin E helps dissolve silybin and increases bioavailability 
- Soluble water extracts
- Silymarin complexes with phospholipids like phosphatidylcholine (Siliphos)
- Liposomal silymarin
- Nano-silymarin or nano-silybin 
- Purified extracts from the fruit 
- Mixing it into small particles (micelles) with bile salts 
- Soft gels 
- Advanced formulations (microemulsions or solid dispersion systems)
- Modifying silybin by binding it to sugars to make it water-soluble (still in the research phase) [129+]
Milk Thistle Safety and Side Effects
Milk thistle and its active component silymarin is a safe herbal product as long as the researched doses are not surpassed.
- Nausea, stomach pain and discomfort (most common)
- Mild diarrhea
- Joint pain
- Skin allergies, itching, and eczema
- Fatigue and insomnia
- Nasal congestion, runny nose, sneezing
- Impotence (rare)
- Anaphylaxis (serious life-threatening allergic reaction) (very rare)
Pregnancy and Children
Although there aren’t enough clinical studies to confirm that milk thistle is completely safe in pregnancy, the studies so far suggest it’s not harmful. Caution is advised in pregnant and breastfeeding women.
Milk thistle is probably safe in children, but more studies are needed. Its use in babies and very small children (<2 years) has not been studied and isn’t recommended .
Milk Thistle for Dogs and Cats
Milk thistle is a great antioxidant that can be safely used in cats and dogs. But the bioavailability is also an issue, as in humans. If you’re looking to use milk thistle for your pets, rather go with a formulation of milk thistle combined with phosphatidylcholine, which has been researched in dogs .
Follow the dosage outlined for humans and adapt it to your cat or dog based on their size/weight.
Although milk thistle generally safe, not much is known about its food and drug interactions .
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Caveats and Limitations
Although there is a fair amount of good quality clinical trials, more research is still needed to confirm many of the listed benefits. Bioavailability was a big issue in some studies, especially in cases of disease when high levels of the active compounds need to reach the blood. Intravenous silybin was used at times, which can’t be considered the same as taking the regular oral supplements. Some studies were only done in animals or in cells.