Psyllium husk is a soluble fiber best known for its potential to improve constipation. But what other contributions can it make to our health? Read on to discover the other fascinating potential benefits and side effects of psyllium husk.
What is Psyllium?
Psyllium is a robust herb that grows around the world but is most commonly found in India, which remains the largest producer of psyllium husk today. It is also referred to as Isabghol (Ispaghol in Pakistan), derived from the Sanskrit words “asp” and “ghol,” together meaning “horse flower.” The whole seed has been used in traditional Iranian medicine for hundreds of years.
The inner seed contains many starches and fatty acids, making it an excellent natural additive for animal feed. The outer coat (the husk) is ground down into mucilage, a term describing clear, colorless, gelatinous dietary fiber that confers the majority of health benefits in both humans and animals .
The gel-like character of mucilage makes it a popular addition to foods to produce desired thickening and texture .
Psyllium husk is largely composed of carbohydrates (85%), with the remainder consisting of fats, plant ash, and protein .
The carbohydrate portion contains twice as much insoluble fiber (cellulose, hemicellulose, lignin) as soluble, both of which are essential to the benefits provided by psyllium husk.
- Soluble fiber: The gel-like material that easily absorbs water, which then causes it to expand
- Insoluble fiber: Consists of the non-digestible, water-resistant plant matter 
Mechanism of Action
The dry, fibrous content of psyllium husk draws water into the gut by pulling water from high- to low-moisture environments.
- The soluble portion easily absorbs water, causing it to expand in the gut. This has the dual effect of softening the stool and physically stimulating gut transport.
- The insoluble fiber is not water absorbent but still helps draw water into the gut and physically stimulates gut flow. It also adds bulk, contributing to larger, firmer stool.
This is the mechanism that psyllium husk is best known for. However, it also binds to muscarinic and 5-HT4 receptors, which would contribute even more to the laxative effect described above .
It may also block calcium channels while activating the NO-cGMP pathway, with the combined effect of decreased gut stimulation. This may explain its paradoxical ability to treat constipation and diarrhea alike .
Health Benefits of Psyllium Husk
Psyllium husk supplements have not been approved by the FDA for medical use; the FDA has, however, approved claims that psyllium husk soluble fiber is associated with reduced risk of coronary heart disease.
In general, dietary supplements lack solid clinical research. Regulations set manufacturing standards for supplements but don’t guarantee that they’re safe or effective. Speak with your doctor before supplementing.
Adding psyllium husk to your diet is proven to reduce constipation by drawing in and absorbing water as it passes through the gut. This causes the stool to soften and expand, making it simultaneously easier to move while stimulating normal gut flow [3, 4].
In multiple small human studies, psyllium husk significantly decreased stool transit time and increased both bulk weight and relative stool softness [5, 3, 6].
This was achieved without disrupting nutrient absorption .
Furthermore, in a multi-site study of 170 patients, psyllium was superior in softening stool and treating chronic constipation than docusate sodium (a stool softener commonly used in healthcare settings) .
A study in rats found that psyllium was more effective than cellulose (insoluble fiber found in most plants) in creating stool moisture, likely due to its soluble fiber content that resists fermentation .
Likely Effective For
2) Heart Disease Prevention
The FDA has approved claims that the soluble fiber found in psyllium husk is associated with reduced risk of coronary heart disease and lower blood cholesterol, provided that people drink enough water at the same time .
Psyllium husk could improve your overall cholesterol profile .
Two clinical trials found lower levels of total and LDL cholesterol, with an increase in HDL [11, 12].
This was observed again in a meta-analysis (21 studies and a total of 1,030 subjects), though it noted the reduction in total cholesterol occurred faster than the drop in LDL. It also indicated that the effects may be dose- and timing-dependent .
The impact of psyllium husk on cholesterol may be explained in part by a small RCT of 20 subjects, which found lowered LDL levels and increased bile acid production after psyllium treatment .
Bile acid production and subsequent excretion is a primary method of eliminating blood cholesterol .
A small clinical trial studied the effects of psyllium husk in 45 teenage males at risk for developing metabolic syndrome. Not only did they observe an improvement in their cholesterol profiles, but there was an improvement in overall body composition/distribution of body fat .
One small RCT of 36 subjects showed that eating fiber and protein provided additive reductions in systolic pressure, averaging 5.9 mmHg with both. These findings were independent of age, gender, weight change, alcohol intake, or urinary sodium/potassium .
A study in rats prone to salt-driven hypertension found smaller increases in pressure when psyllium husk was added to the diet and proposed that this was due to the psyllium causing increased fecal excretion of sodium .
A separate clinical trial following 72 healthy people on a regular diet compared fiber and healthy diet separately against placebo for 12 weeks. It showed that psyllium husk alone initially lowered systolic and diastolic pressures but the effect did not last for the full 12 weeks, whereas healthy diet alone had lasting effects and created larger improvements in blood pressure .
Possibly Effective For
Psyllium husk may also relieve diarrhea, which may seem strange considering its long-proven role in reducing constipation .
In 2 human studies (with as many as 39 subjects), psyllium husk increased stool transit time and improved the consistency of the stool in patients with diarrhea. In the same studies, patients with constipation had decreased transit time [21, 22].
While the mechanism for controlling diarrhea is less understood, this study in living mice (in addition to rabbit/pig guts) may shed some light:
- Psyllium husk treated constipation in mice. But, it also stimulated muscarinic and 5-HT4 receptors of the gut, which would complement the physical stimulation it produces.
- When psyllium husk was given to mice with diarrhea, transit time was slowed and stool consistency improved. Receptor pathways were changed in these mice as well, specifically blocking calcium ion channels and activation of the NO-cGMP pathways, which would combine to inhibit gut flow .
With that information in mind, it may help to think of psyllium husk as a “regulatory” fiber rather than strictly anti-diarrheal or anti-constipation. This makes it an excellent option for patients with irritable bowel syndrome, who often have diarrhea and constipation.
A randomized controlled pilot study evaluated psyllium husk in 60 cancer patients with radiation-induced diarrhea, showing a decrease in both the incidence of diarrhea and the severity of symptoms .
Sometimes diarrhea is an unavoidable side-effect of another medication. Patients with liver failure may have a liver-caused brain injury, where ammonia builds up in the blood and causes altered mental status. This is treated with lactulose, which can cause significant amounts of diarrhea .
A randomized crossover study of 8 patients showed that psyllium husk delayed stomach emptying and reduced the speed of gut transit, possibly due to the poor fermentation of psyllium husk compared to other fibers .
5) Blood Sugar
Multiple types of fiber have been found to decrease blood sugar .
In multiple double- and single-blind RCTs (with as many as 125 subjects), psyllium husk significantly reduced both fasting and after-meal blood sugar levels, reduced insulin spikes, and decreased the absorption of glucose, with a reduction in HbA1c [26, 12, 27, 28, 11, 29].
Similar results were seen in a meta-analysis of 7 studies of 378 patients, including 3 that were randomized and blinded .
In a small DB-RCT of 49 patients, psyllium husk not only improved fasting blood sugar and HbA1c levels but enhanced patient tolerance to metformin (a very common oral medication for treating type 2 diabetes) .
It is important to note that these results were achieved when psyllium husk was consumed with meals. The FDA has not approved psyllium for the purpose of decreasing blood sugar; additional research will be required.
6) Healthy Weight
Psyllium husk may be able to help with weight loss by increasing fullness .
In a 200-subject DB-RCT, consuming psyllium husk with meals increased fullness and reduced subjective appetite sensation, resulting in weight loss (approximately 10 lbs) .
The mechanism behind this may be explained by a small RCT of 12 patients that found that psyllium delayed stomach emptying, which likely contributes to the increased fullness and reduced appetite .
Another triple-blind study of 17 women revealed the same changes in fullness and appetite and found that subjects inherently reduced their daily fat intake .
Not only is psyllium husk associated with weight loss, but another double-blind RCT study of 72 patients showed that it reduced BMI and total body fat percentage. The study does note that while this was achieved with psyllium husk alone, combining it with a healthy diet produced superior results .
The FDA has not approved psyllium for the purposes of weight loss. If you want to lose weight, talk to your doctor about the best strategies for you, which may include exercise and diet changes.
7) Irritable Bowel Syndrome
We know psyllium husk has a role in treating both diarrhea and constipation, as previously stated. These are also symptoms of irritable bowel syndrome and ulcerative colitis .
One study of 28 subjects looked specifically at whether psyllium husk plays a role in patients with irritable bowel syndrome, discovering that psyllium husk eliminated symptoms and further showing that stopping psyllium husk causes a relapse .
A placebo-controlled trial of 29 subjects with ulcerative colitis in remission found superior control of gut symptoms using psyllium husk vs. placebo. Four patients were unable to finish the trial due to relapse, noting that three were in the placebo category .
Though promising, these results are not considered sufficient evidence of psyllium’s benefits for IBS. Additional research and larger studies will be required to confirm these effects.
Cell Studies (Lacking Evidence)
No clinical evidence supports the use of psyllium for any of the conditions listed in this section. Below is a summary of the existing cell-based research, which should guide further investigational efforts. However, the studies listed below should not be interpreted as supportive of any health benefit.
8) Anti-Amoebic Activity
A study in cells found that a water- and petroleum-based husk extract inhibited 3 Entamoeba species, including histolytica, which causes a wide array of symptoms in humans. The petroleum-based extract showed much greater inhibition of growth .
Additional research will be required to determine whether psyllium has any benefit against Entamoeba infection (amebiasis) in animals or humans.
In a study of rats exposed to a known colon carcinogen (cancer-causing chemical), psyllium husk strongly reduced the incidence of tumors, compared to cellulose and control .
This effect has not been studied in humans, and a single rat study should never be considered grounds to use any substance for the purpose of fighting cancer.
Overall, psyllium husk is associated with very few side effects. The most common finding is some mild, temporary gut discomfort [11, 39, 40, 41].
However, there are several case reports that you should know about.
- Two studies found a total of 11 nurses with occupational asthma linked to psyllium exposure:
- One looked at 5 nurses who had symptoms after preparing psyllium husk solutions for patients. They had all tested positive for IgE antibodies to psyllium, and inhalation challenges produced symptoms in all of them. One patient had reactive airway closure and required 3 hours of assisted ventilation .
- The other study looked to see if nurses with known exposure reactions could have a reaction to ingestion. All 6 developed airway symptoms, one requiring urgent intervention .
- One case study of a 40-year-old woman who had been taking a psyllium-containing laxative for 2 years found that the woman developed a whole-body itching (pruritic) rash, sparing only her face. The symptoms resolved when psyllium was stopped and started again with an oral challenge. She was IgE positive for psyllium antibodies. She underwent sensitization therapy to allow her to continue using the laxative. It is important to note that her sensitivity was protein-based and likely due to inner seed exposure, rather than the husk .
- One case study of a patient on oral lithium (a medication used to treat bipolar disorder) experienced a drop in blood lithium levels while taking psyllium husk, which returned to normal after cessation of psyllium .
- Four patients developed small bowel obstruction after psyllium was used as an oral contrast agent for CT or MRI scans. The takeaway was that caution must be used when considering psyllium husk in anyone with suspected bowel strictures or active inflammation .
Limitations and Caveats
Most of the studies were done in humans and even include meta-analyses, but overall the sample sizes in these studies were small and sometimes limited by gender or other restrictions. Care should thus be taken when considering psyllium husk therapy (as you should with any supplement).
The FDA has approved claims that psyllium husk soluble fiber is associated with reduced risk of coronary heart disease. Other potential health benefits require additional research.
As mentioned above, there is a case report of psyllium interfering with lithium absorption .
It may also delay digoxin (a common heart failure medication) absorption, but is unlikely to prevent it or cause any clinically significant effect .
The LexiComp Drug Interactions used by physicians to screen for drug interactions gives psyllium/digoxin a B risk rating, meaning they may interact with each other but no action is needed as there is little concerning evidence .
Other sources suggest that psyllium may interfere with the absorption of tricyclic antidepressants (amitriptyline, doxepin, imipramine), seizure medications (carbamazepine), bile acid sequestrants (cholestyramine, colestipol), and a variety of diabetes medications.
Sources and Supplementation
Where Can I Find It?
Psyllium husk is sold over the counter in the whole form, granulated, encapsulated, or powdered. Because it lacks a distinct flavor, functions as a food thickener, and stores easily, psyllium has been fortified into many food products, especially ice cream and high-fiber cereals .
The Lexicomp drug database recommends the following dosages:
- For constipation: 2.5 to 30 g/day in divided doses (In children age 6 to 11 years old: 1.25 to 15 g/day in divided doses).
- For reduction of coronary heart disease: At least 10.2 g/day (translates to at least 7g soluble fiber/day)
- For adjunctive therapy of type 2 diabetes: 6.8 to 13.6 g/day split between 2 doses
- For irritable bowel syndrome: 10 g/day over 1 or 2 doses 
Bagged, Whole Husks:
- People find that mixing whole husks in liquid produces a thick, grainy substance that is difficult to consume unless they finish it quickly. However, they say it is less likely to get stuck in your teeth and on the glass than the powder.
- A user who added it to their cooking found the husks much more palatable, especially in gluten-free cooking or on a dry cereal with fruit.
- Multiple users endorse improvement in their stool form with whole husks, requiring less toilet paper.
- Users generally find the capsules easy to use and work with compared to the bagged whole husks or powder, especially when trying to make a drink.
- People appreciate the lack of artificial sweeteners.
- Again, users state that psyllium capsules support their stool regularity.
Powdered Psyllium Husk:
- Many users add a spoonful to their water or on food to get their daily fiber intake.
- One user compared it to Metamucil in effectiveness but appreciated the lack of sugar in the psyllium powder.
- Multiple users say they dislike the texture it produces when mixed in liquids and must be consumed quickly, with one person describing it as “a raw egg texture.”
- Another user stated appreciated that it had no foul taste and wasn’t too bulky, adding it to their hot cereal in the morning.
- Users state that the powder is helpful in maintaining bowel regularity.
Summary: Psyllium can be difficult to consume in a drink, and if you choose to do so, people recommend drinking it quickly before it thickens. Alternatively, have it over food that takes well to thickening (oatmeal, for example). Experiences with encapsulated psyllium seem to be positive overall.
Psyllium husk is the outer coating of the psyllium seed. It is rich in soluble and insoluble fibers, the consumption of which is associated with a reduced risk of coronary heart disease. Psyllium husk is also often used to soften the stool, and it may have other health benefits that require further study.