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CBD Side Effects: What Studies Really Show
Key Takeaway: CBD is considered well-tolerated according to the WHO, but can cause side effects such as fatigue, dry mouth and gastrointestinal complaints. The most important safety concern involves drug interactions via the liver's CYP450 enzyme system. Not medical advice.
The key facts:
- WHO assessment: CBD is generally well-tolerated and safe
- Most common side effects: fatigue, dry mouth, diarrhoea, appetite changes
- CBD inhibits CYP450 liver enzymes — drug interactions possible
- Mental health: no intoxication, no addiction potential; rarely irritability
- Dose-dependent: most side effects occur at high doses and are reversible
At a glance:
| Fact | Detail |
|---|---|
| WHO assessment | CBD is generally well-tolerated and safe |
| Most common side effects | Fatigue, dry mouth, diarrhoea, appetite changes |
| Liver interaction | CBD inhibits CYP3A4, CYP2C9, CYP2C19, CYP2D6 |
| Mental health | No intoxication, no dependence; rarely irritability |
| Heart palpitations | Rare, mainly at high doses or with stimulants |
| Risk groups | Pregnant women, children, liver disease, medication users |
CBD — short for cannabidiol — is one of the most widely used cannabinoids. It is often marketed as having "few side effects". The WHO classifies CBD as generally well-tolerated. But like any active substance, there are possible CBD side effects you should be aware of, especially if you take medications or belong to a risk group. You'll find an overview of CBD effects in our dedicated guide.
Note: This article is for informational purposes only and does not replace medical advice. For health-related questions, consult a doctor or pharmacist.
Common CBD Side Effects: What Research Has Documented
Most CBD oil side effects are considered mild. They mainly occur at higher doses and are generally reversible — they disappear with a reduced dose or after discontinuation.
Fatigue and Drowsiness
The most common side effect is increased fatigue. In a study of 72 adults, some participants reported drowsiness [Shannon et al., 2019]. This occurred particularly at the beginning of use. The effect is dose-dependent: higher doses (from about 150 mg) tend to cause more fatigue. At low doses (10–25 mg), some even report increased alertness.
According to CBD side effects experiences from many users, fatigue often normalises after the first few days. If you're taking CBD for the first time, it's best to do so in the evening and observe your reaction.
Dry Mouth
CBD can affect saliva production. Many users report a dry mouth. This effect likely operates through the cannabinoid receptors in the salivary glands. Drinking more water can significantly alleviate this issue.
Gastrointestinal Complaints
Diarrhoea, nausea and stomach discomfort are among the well-known CBD oil side effects. They occur more frequently at higher doses. Sometimes the carrier oils are the cause — MCT oil or hemp seed oil are not well tolerated by everyone. Taking CBD with food can reduce stomach problems.
Appetite Changes
Both decreased and increased appetite are reported with CBD. Unlike THC, CBD does not specifically stimulate appetite. The effect varies considerably from person to person.
CBD Side Effects on the Liver: The CYP450 Enzyme System
CBD side effects on the liver are the most important safety aspect — and the most frequently underestimated.
How CBD Affects Liver Metabolism
CBD is metabolised in the liver via the CYP450 enzyme system — the same system that breaks down most prescription medications. Studies show that CBD inhibits the following enzymes [Nasrin et al., 2021]:
- CYP3A4 — the most important liver enzyme, metabolising approximately 50% of all medications
- CYP2C9 — metabolises warfarin (blood thinner) and NSAIDs, among others
- CYP2C19 — strongest inhibition by CBD; affects clopidogrel and some antidepressants
- CYP2D6 — metabolises numerous antidepressants and beta-blockers
- CYP2B6 — affects bupropion and some antiretrovirals, among others
Liver Enzyme Levels at High Doses
At very high doses, elevated liver values (ALT, AST) have been found. These doses are significantly above the usual range and primarily affect the medication Epidyolex, used for certain forms of epilepsy at doses up to 20 mg/kg/day.
At typical CBD oil doses (20–80 mg/day), no clinically relevant liver damage is known. Nevertheless, people with pre-existing liver conditions should exercise particular caution.
The Grapefruit Rule
A practical rule of thumb: if a medication carries a grapefruit warning, caution is also warranted with CBD. Both inhibit similar CYP450 liver enzymes.
Drug Interactions
A large review study found 20 groups of medications with documented cannabis interactions [Ho et al., 2024]. The most important involve:
| Medication Group | Type of Interaction | Risk |
|---|---|---|
| Antiepileptics (e.g. clobazam, valproate) | Increased levels, more side effects | High |
| Blood thinners (e.g. warfarin) | Enhanced anticoagulation | High |
| Immunosuppressants (e.g. tacrolimus) | Enhanced effect | High |
| Benzodiazepines | Enhanced sedation | Medium |
| Antidepressants (SSRIs, TCAs) | Altered levels | Medium |
| Beta-blockers | Enhanced effect | Medium |
| Opioids | Enhanced sedation | Medium |
| Blood sugar medications | Hypoglycaemia risk | Medium |
A recent review emphasises that interactions with clobazam, warfarin and tacrolimus are well documented [Hossain et al., 2024]. CBD can also interact with alcohol and other substances [Balachandran et al., 2021].
Important: If you take medications, you should only use CBD after consulting your doctor.
CBD Side Effects on the Brain: Effects on the Nervous System
The question of CBD side effects on the brain concerns many people. The key distinction from THC is important: CBD does not produce intoxication and does not impair mental performance the way THC does.
What CBD Does in the Brain
CBD acts on the endocannabinoid system, serotonin receptors (5-HT1A) and vanilloid receptors (TRPV1) [Blessing et al., 2015]. This can influence mood, pain and stress.
Laboratory studies suggest that CBD may protect nerve cells [Atalay et al., 2020]. However, these results come from animal models and cell cultures. Long-term studies on CBD's influence on the human brain are still lacking.
Dizziness and Light-headedness
In isolated cases, users report dizziness or mild light-headedness, particularly at higher doses. This could partly be related to CBD's blood pressure-lowering effect.
CBD Side Effects on Mental Health: Mood, Anxiety and Irritability
CBD side effects on mental health are a frequently searched topic. Most studies describe CBD as mood-balancing. A meta-analysis of 316 participants gave CBD a good safety profile for anxiety symptoms [Ribeiro et al., 2024]. Kayser et al. showed in a double-blind study that CBD significantly reduced worry in highly anxious individuals [Kayser et al., 2023].
Nevertheless, there are isolated reports of:
- Irritability: particularly at high doses or with individual intolerance
- Mood deterioration: in rare cases; the evidence base is thin
- Vivid dreams: some users report altered dream experiences
These effects are not well studied. It is unclear whether they come directly from CBD. Shannon et al. showed that anxiety scores decreased in 79.2% of participants on CBD [Shannon et al., 2019], which speaks more in favour of positive mental health effects.
Important: CBD is not a substitute for psychotherapeutic or psychiatric treatment. For serious mental health concerns, always consult a doctor.
CBD Side Effects — Heart Palpitations: What's Behind It?
The topic of CBD heart palpitations causes concern for some users. The evidence is nuanced:
- CBD alone is not associated with an increased heart rate in most studies. On the contrary, some research suggests a slight blood pressure-lowering effect.
- Heart palpitation reports in forums often have other causes: individual sensitivity, anxiety during first use, interaction with caffeine, or products containing THC.
- Blood pressure drop: CBD can lower blood pressure. The body sometimes compensates with a faster pulse — this is the baroreflex.
For cardiovascular conditions or blood pressure-lowering medications, a medical consultation before taking CBD is advisable.
WHO Safety Profile and Long-term Data
The WHO classified CBD in 2017 as "generally well-tolerated with a good safety profile". The key findings:
- No abuse potential: CBD does not create dependence
- No tolerance development: Users do not need to increase the dose over time
- No withdrawal symptoms: Stopping CBD does not cause withdrawal effects
- No lethal dose: No death from CBD overdose has been documented
Limitations of Long-term Data
Most CBD studies run for weeks to a few months. Long-term studies spanning years are lacking. Open questions include:
- Long-term effects on liver function with prolonged use
- Possible effects on the hormonal system
- Effects on the immune system with long-term use
Novel Food Status
CBD does not have Novel Food authorisation in the EU. EFSA proposed a safe daily dose of just 2 mg in September 2025 — far below the amounts used in studies and by consumers. In the UK, the Food Standards Agency (FSA) has set a similar cautious approach, recommending no more than 70 mg of CBD per day for healthy adults.
Special Risk Groups
For certain groups of people, enhanced precautions apply:
- Pregnant and breastfeeding women: Insufficient study data on safety. Use is advised against.
- Children and adolescents: CBD is only approved for children as a prescription medication (Epidyolex) for certain forms of epilepsy. Over-the-counter CBD products should not be given to children.
- People with liver disease: Enhanced caution due to hepatic metabolism.
- People with low blood pressure: The blood pressure-lowering effect can cause dizziness.
- Medication users: Interactions via the CYP450 system possible (see above).
How to Minimise CBD Side Effects
- Start low, go slow: Begin with 5–10 mg and increase gradually over days
- Choose quality products: Products with independent lab analyses (COA) reduce the risk of contamination
- Inform your doctor: Especially when taking medications — have interactions checked
- Take with food: Taking CBD with fatty foods can reduce stomach complaints
- Listen to your body: Fatigue or digestive issues? Reduce the dose and observe
- Avoid alcohol: Combining CBD and alcohol can enhance the sedative effect
- Keep a diary: Recording dose, timing and how you feel helps find the optimal dosage
For more on proper dosing, see our guide: CBD Dosage: Finding the Right Amount.
Conclusion
CBD is generally well-tolerated. The WHO confirms this. Serious side effects are rare. Fatigue, dry mouth and stomach problems are the most common CBD side effects. They are mostly mild and dose-dependent. The biggest concern is drug interactions via CYP450 liver enzymes. If you take medications, consult your doctor first. CBD effects on mental health and the brain are currently considered minimal. CBD does not cause intoxication and is not addictive.
Quality CBD products with lab analyses: At Cannabuben, you'll find CBD oils with independent lab reports and EU-wide shipping. View CBD products at Cannabuben{rel="nofollow sponsored"} Affiliate link.
Note: This article is for informational purposes only and does not replace medical advice. For health concerns, please consult a doctor or pharmacist. The side effects and interactions described may vary between individuals.
Frequently Asked Questions
What are the side effects of CBD oil drops? The most common CBD oil side effects are fatigue, dry mouth, diarrhoea and appetite changes. They mainly occur at higher doses and are generally mild and temporary. At usual doses (20–40 mg/day), most users report few to no side effects.
Is CBD harmful to the liver? At usual doses, there is no evidence of clinically significant liver damage. Very high doses — such as those used with the prescription medication Epidyolex (up to 20 mg/kg/day) — can increase liver enzyme levels. CBD also inhibits CYP450 enzymes, which can affect drug metabolism [Nasrin et al., 2021]. People with liver disease should exercise particular caution.
Can CBD cause heart palpitations? Heart palpitations are not a typical CBD side effect. In rare cases, CBD's blood pressure-lowering effect may lead to a slight compensatory increase in heart rate (baroreflex). Palpitation reports are more often related to interactions with stimulants, individual sensitivity, or contaminated products with elevated THC content.
Does CBD negatively affect mental health? Current evidence points to positive mental health effects of CBD: significant reduction in anxiety symptoms [Ribeiro et al., 2024] and worry [Kayser et al., 2023]. Isolated cases of irritability are reported, particularly at high doses. CBD does not cause intoxication and has no addictive potential.
Can CBD interact with medications? Yes. CBD inhibits important liver enzymes of the CYP450 system involved in the breakdown of many medications. Clinically significant interactions are particularly documented with blood thinners (warfarin), antiepileptics (clobazam) and immunosuppressants (tacrolimus) [Hossain et al., 2024]. Rule of thumb: if your medication carries a grapefruit warning, caution is also warranted with CBD.
Does CBD have effects on the brain? CBD interacts with the endocannabinoid system, serotonin receptors and vanilloid receptors in the brain [Blessing et al., 2015]. Preclinical studies suggest neuroprotective properties [Atalay et al., 2020]. CBD does not impair cognitive performance and does not cause intoxication. Long-term studies on effects on the human brain are still lacking.
Sources
- Shannon, S. et al. (2019). Cannabidiol in Anxiety and Sleep: A Large Case Series. Permanente J, 23. PubMed
- Nasrin, S. et al. (2021). Cannabidiol selectively inhibits the function of human cytochrome P450 enzymes. AAPS J. PubMed
- Balachandran, P. et al. (2021). Cannabidiol Interactions with Medications, Illicit Substances, and Alcohol. J Cannabis Res. PMC
- Ho, T.C. et al. (2024). Cannabis Drug Interactions: A Systematic Review. Clin Transl Sci. PMC
- Hossain, K.R. et al. (2024). THC and CBD Drug-Drug Interactions: A Systematic Review. Front Pharmacol. Frontiers
- Blessing, E.M. et al. (2015). Cannabidiol as a Potential Treatment for Anxiety Disorders. Neurotherapeutics, 12(4). PubMed
- Atalay, S. et al. (2020). Antioxidative and Anti-Inflammatory Properties of Cannabidiol. Antioxidants, 9(1). PubMed
- Ribeiro, L.H.L. et al. (2024). CBD and anxiety: systematic review and meta-analysis. Life. PubMed
- Kayser, R.R. et al. (2023). CBD reduces worry in high trait-worry individuals. J Psychopharmacol. PubMed
