CBD oil is generally safe and well-tolerated, but it is not free of side effects. Read on to learn which adverse effects you should watch out for when using CBD oil, how the delivery form influences them, and what you can do to reduce your risk.

CBD Oil Side Effects

With the recent legalization of CBD oil in many states worldwide, its popularity is booming and people are using it for conditions such as [1]:

An advantage of CBD oil is that it’s generally safer and causes fewer adverse effects than the drugs typically used for these conditions. Chronic doses of up to 1500 mg/day were tolerated well in multiple studies [2+, 3].

Unlike THC, CBD doesn’t cause behavioral and psychological side effects. What’s more, it may even reduce some of them such as anxiety, psychosis, and memory loss [4, 5, 6, 7].

CBD oil causes fewer side effects than THC and most prescription drugs, even at high doses.

Nevertheless, there are some potential side effects of CBD oil that you should watch out for. Below is a detailed overview of the most common ones.

1) Dry Mouth

Whether you use them for recreational or medicinal purposes, cannabis products will often make your mouth feel as if it were stuffed with cotton balls. Almost 12% of 1500 people responding to a survey about CBD use experienced dry mouth, making it the most common adverse effect [1].

Stimulation of the CB1 and CB2 receptors in the salivary glands reduces saliva secretion, which makes your mouth feel dry. The well-known cannabis compound THC activates these receptors directly. In turn, CBD raises the levels of an activator naturally produced in the body–the cannabinoid anandamide [8, 9, 10, 11].

About one in ten people who use CBD oil (or cannabis products) will experience dry mouth.

2) Digestive Issues

Both CBD oil supplements and the FDA-approved CBD medicine Epidiolex have been reported to cause digestive issues such as [1, 3]:

  • Nausea and vomiting
  • Diarrhea
  • Increased or reduced appetite
  • Weight loss or gain

Because preliminary research suggests that CBD improves rather than causes nausea and diarrhea, these effects most likely result from the irritating effects of other ingredients (e.g., carrier oils) on the bowels [12, 13, 14].

Alternatively, the loose regulation of supplements may allow for excessive CBD levels in products or harmful contaminants such as pesticides, heavy metals, and solvents [15+, 16+].

In turn, the endocannabinoid system has a proven role in promoting appetite. The mixed effects of CBD on appetite and weight seen in different studies may be due to its dual effect: it blocks the CB1 and CB2 receptors but boosts the levels of their activator anandamide [17, 18, 10].

Contaminants and additives are likely responsible for the digestive side effects of low-quality CBD oil: nausea, vomiting, diarrhea, and appetite and weight changes.

3) Drowsiness and Fatigue

People taking CBD oil often report feeling sleepy and tired. Indeed, this side effect was observed in early clinical trials and one of the most common uses of CBD oil is to improve sleep disorders [19+].

If the symptoms are very severe, you shouldn’t drive or operate heavy machinery.

The effect of CBD on sleep is biphasic: high doses increase sleeping time, lower amounts promote wakefulness. Additionally, levels of endocannabinoid receptors depend on the circadian rhythm. This may explain why CBD tends to cause drowsiness later in the day but has the opposite effect in the morning [20, 21, 22].

CBD oil may make you feel sleepy, especially if you take high doses at night. Low morning doses, on the contrary, increase wakefulness.

4) Dizziness

High doses of CBD lowered blood pressure in a small trial on 9 people. In turn, THC has a more complex effect: it slightly raises blood pressure in people lying down but increases the risk of sudden blood pressure drops when standing up [23, 24+].

As a result, a common adverse effect of CBD–both alone and with equal amounts of THC (nabiximols)–is feeling dizzy and light-headed [25, 26, 27].

If your blood pressure drops too much, you may faint. The risk is especially high in people diagnosed with low blood pressure or on blood pressure medications–such as diuretics, ACE inhibitors, and beta-blockers.

CBD oil, alone or with THC, may reduce blood pressure. This can make you feel dizzy and light-headed, especially if you are prone to blood pressure drops.

5) Possible Liver Damage

Several trials testing CBD for seizures found possible liver damage (high transaminases ALT and AST) in 9-25% of the people. The risk increased with the dose and was highest in people also taking the anti-seizure drug valproate, which is known to cause liver injuries [28+, 29, 30, 31, 32, 33].

Similarly, CBD caused signs of liver toxicity (high transaminases, alkaline phosphatase, and bilirubin) in mice and dogs. However, the doses were generally higher than those used in human trials [34, 35, 36].

CBD oil may cause liver damage at very high doses and in people prescribed the anti-seizure drug valproate.

6) Irritability

CBD is often used to curb anxiety, although it has “inverted U-shaped” effects: moderate doses are effective for a range of anxiety disorders and stressful situations, while low or high amounts aren’t [37, 38].

In turn, very high doses may even trigger anxiety and irritability. This was the case in 7-9% of the children in 2 clinical trials using CBD for seizures and autism [39, 40].

The effect probably involves the TRPV1 receptor, the activation of which increases the brain’s response to stressful situations [41].

CBD boosts the naturally-produced cannabinoid anandamide. While moderate anandamide levels activate CB1 receptors and curb anxiety, high amounts may worsen it by binding to TRPV1. CBD also activates this receptor directly, further contributing to the anxiety-triggering effects [42, 43, 10, 44].

Low-to-moderate CBD oil doses reduce anxiety, but high doses can worsen it.

7) Immune Suppression

CBD reduces the immune response. It prevents T cells from dividing, migrating to inflammation sites, and producing pro-inflammatory cytokines. This may be beneficial in people with autoimmune conditions such as rheumatoid arthritis or multiple sclerosis [45, 46, 47, 48, 49, 50, 51].

The downside of blocking the immune response is that it may make people with weakened immune systems more prone to infections. Thus, people on immunosuppressants or with conditions such as HIV, diabetes, and Down syndrome might want to avoid it [52].

CBD oil reduces the immune response, which may make people with a weak immune system more prone to infections.

Kidney Health

CBD didn’t damage the kidneys in clinical trials. In fact, it protected against kidney injury and inflammation in numerous animal studies [53, 54, 55, 56, 57].

Though more clinical trials are needed, the current evidence suggests CBD oil will not harm your kidneys at normal doses.

On the other hand, people with kidney disease should probably avoid THC-containing medical marijuana without consulting a doctor.

According to a recent review, THC may worsen kidney health and increase urination by activating CB1 receptors. Remember that, unlike THC, CBD blocks these receptors. However, CBD may indirectly activate them by increasing anandamide levels in the body [58+].

Lastly, avoid synthetic cannabinoids at all costs (products like “spice” and “K2” sold in smoke shops). These chemicals caused sudden and severe kidney injury in several cases [58+].

Unlike THC and synthetic cannabinoids, CBD oil probably does not cause side effects on the kidneys; it might even be protective.

Are You at Risk of CBD Oil Side Effects?

Risk Populations

CBD altered the levels of two drug transporters in placental cells. This suggests that taking CBD oil during pregnancy may increase the exposure of the fetus to any drugs that the mother takes. Pregnant women should avoid CBD oil in any case, since safety data are lacking [59].

Taking THC-containing CBD oil during pregnancy and breastfeeding is particularly dangerous, since THC may reduce growth and cause brain developmental anomalies in babies [60+].

Because there are no studies testing its safety in children below 2 years old, it’s better to avoid giving them CBD oil unless prescribed by a doctor.

CBD is safe in older children, but they may be more sensitive to THC and toxic contaminants such as heavy metals and pesticides than adults. Be sure to use high-quality, THC-free CBD in children and consult the doctor first.

Pregnant women and children under 2 years old should avoid CBD oil due to the lack of safety data; THC during pregnancy is known to be dangerous.

Drug Interactions

Most drugs are broken down by liver enzymes. Among them, cytochrome (CYP) P450 plays a key role. A single CBD dose blocks several CYP enzymes, such as:

By doing so, it may slow the breakdown of several drugs and enhance their effects [61, 62, 63, 64, 65].

Indeed, CBD reduced the breakdown of the sedative hexobarbital, the anti-seizure drug clobazam, and the blood thinner warfarin in humans. It had the same effect on the immunosuppressant cyclosporin and the cannabis compound THC in cells [66, 67, 68, 69].

On the other hand, repeated CBD doses can increase the levels of some enzymes of this group and reduce the effects of the drugs they break down [70, 71, 72, 73].

Plus, CBD itself is broken down by CYP enzymes, especially by CYP34A and CYP2C19. Drugs that block these enzymes (such as ketoconazole and ritonavir) will enhance its effects, while those that activate them (such as phenobarbital and rifampicin) will have the opposite effect [74, 3].

If you are on prescription medication and plan to use CBD oil, ask your doctor about potential interactions and dose readjustment. Additionally, avoid combining CBD oil with grapefruit or other supplements that block the same liver enzymes (such as St John’s wort or watercress).

CBD oil can block or activate liver enzymes that metabolize drugs. This may increase the side effects of both CBD oil and the medication you’re taking.

How Does the Delivery Form Influence CBD Oil Side Effects?

Oral

While rapid-release forms (mouth sprays and oil tinctures) deliver CBD directly into your bloodstream, slow-release forms (capsules, edibles, and teas) have to pass your digestive system first. This means their ingredients may irritate your bowels and give you nausea and diarrhea [75+, 76].

However, rapid-release forms will release CBD faster, so you may experience both wanted and unwanted effects sooner [75+, 76].

And since tinctures and sprays are directly applied in the mouth, they will quickly reach the salivary glands and cause dry mouth. Mouth sprays may also cause a stinging sensation and even burns, especially if they contain alcohol [8, 77].

Capsules and edibles are more likely to cause digestive side effects, while mouth sprays and tinctures more frequently cause dry mouth.

Vapes

Vapes bypass the digestive system without irritating your bowels, but they trigger the other adverse effects faster [75+, 76].

Vaping is considered safer than smoking cigarettes or joints because the oil is heated at lower temperatures that produce fewer toxic byproducts [75+ 78].

However, the additives used as flavorings and thinning agents in vaping oils may still pose some hazards. Although they are normally food-grade, they release harmful compounds (including the cancer-causing formaldehyde) when vaporized. Their heavy use may lead to [79, 78, 80+]:

  • Cough
  • Dry throat
  • Lung injury
  • Fat particles entering the lungs (lipoid pneumonia–rare)

For instance, one man developed severe lung damage from vaping CBD oil [81+].

Additives in CBD oil may cause cough, dry throat, and lung damage when vaped.

Creams & Gels

Creams and gels act locally on the application site and don’t release CBD into the gut or bloodstream. This means they will not cause most of the adverse effects previously described [75+].

In turn, they may cause allergic reactions with itching, redness, and rashes on the skin. It’s important to note that the reactions can be caused by either CBD or other ingredients in the formulation [82+, 83+].

Creams and gels with CBD oil may cause allergic skin reactions in some people.

How to Reduce Your Risk of Side Effects from CBD Oil

1) Drink More Water

The best way to reduce dry mouth when using CBD oil is to drink plenty of water and other hydrating liquids before, during, and after consumption.

2) Find Additive-Free Products

You can reduce the risk of digestive issues by choosing forms that bypass the gut and directly release CBD into your bloodstream such as vapes, mouth sprays, and oil tinctures. High-quality oils without additives may also irritate your bowels less.

3) Take it Before Sleep

If you feel drowsy or light-headed after taking CBD oil, you may need to reduce the dose or take it only before sleep.

4) Increase Wakefulness Naturally

Drinking coffee or tea will help you both stay awake and raise your blood pressure, but it also causes many side effects. Try to get more sunlight in first thing in the morning, as it will energize you and help you get better sleep at night. We talk about other natural ways to increase wakefulness in this post.

5) Support Your Liver

Avoid combining CBD with the anti-seizure drug valproate. Additionally, make sure not to exceed the dose and regularly monitor your liver function to reduce your risk of liver damage. Eggs (choline), artichokes, NAC, and probiotics also support liver health. Read more foods and supplements that are good for the liver here.

6) Don’t Take Megadoses

Only very high CBD doses may cause irritability. Make sure not to exceed the dose and try reducing it if you notice this symptom.

7) Monitor Your Immune Response

If you have a weakened immune system, you should consult your doctor before taking CBD oil. You may need to avoid CBD or take a lower dose.

Additionally, you may also want to look into balancing your Th1/Th2 immune response. If you have a slightly weaker immune system and are prone to allergies, you are probably Th2-dominant.

To reduce your risk of CBD oil side effects, avoid products with additives, drink plenty of water, get sunlight during the day, and support your liver and gut health.

Buy CBD Oil

Vendors sell CBD oil on Amazon, but many of them do not fulfill quality standards. Some don’t even specify the CBD content in their products, while others sell hemp oil with little or no CBD. Most of these vendors are not to be trusted.

We recommend the following brand, which specifies quality procedures and CBD content in their products:

This section contains sponsored links, which means that we may receive a small percentage of profit from your purchase, while the price remains the same to you. The proceeds from your purchase support our research and work. Thanks for your support.

Takeaway

CBD oil is safe and most people tolerate it well.

Low-quality products may contain additives and toxins that can irritate the lungs when vaped and the gut when taken orally. Choose high-quality products to reduce your risk.

Additionally, CBD oil can make you feel drowsy and lightheaded. If you feel tired after taking CBD oil, lower your dose or use it only before sleep. Look to also increase your wakefulness naturally by getting more sunlight during the day.

High doses may damage the liver, but likely only in people taking the anti-seizure medication valproate. Monitor your liver enzymes and look into natural ways to protect your liver.

Avoid CBD oil if you have a weak immune system, as it might make you more prone to infection.

If you take prescription drugs, consult your doctor. Many drugs can interact with CBD oil and increase the risk of side effects.

Pregnant women and children should avoid CBD oil until more safety data are available.

About the Author

Carlos Tello, PhD (Molecular Biology)

PhD (Molecular Biology)

Carlos received his PhD and MS from the Universidad de Sevilla.

Carlos spent 9 years in the laboratory investigating mineral transport in plants. He then started working as a freelancer, mainly in science writing, editing, and consulting. Carlos is passionate about learning the mechanisms behind biological processes and communicating science to both academic and non-academic audiences. He strongly believes that scientific literacy is crucial to maintain a healthy lifestyle and avoid falling for scams.

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