CBD has a good safety profile. That's what the World Health Organization has concluded since 2018. But "good safety profile" doesn't mean "no risk": like any substance active in the body, CBD can cause side effects, and it interacts with common medicines. That's not a reason to panic. It's a reason to know precisely what to expect.
This file brings together what clinical trials and systematic reviews have documented: the common, mild effects, the one genuinely serious signal, the drug interactions worth knowing, the groups who should abstain, and what you actually risk with non-compliant products — the real danger today, far more than CBD itself.
Key points — The most common CBD side effects are drowsiness, fatigue, diarrhoea and appetite changes. The one serious signal documented is raised liver enzymes, seen at high pharmaceutical quantities, especially combined with certain anti-epileptic drugs. CBD is processed by the CYP3A4 and CYP2C19 enzymes, which also metabolize anticoagulants, anti-epileptics and immunosuppressants: anyone on medication should ask for medical advice before using it. Pregnancy, breastfeeding, being a minor and liver impairment call for abstaining. The most concrete risk in 2026 comes from mislabeled or adulterated products, not from compliant flowers and resins.
What clinical trials show: the common effects
The most cited synthesis on the subject is by Iffland and Grotenhermen, published in 2017 in Cannabis and Cannabinoid Research. It confirms a favorable safety profile in humans, while listing the most regularly reported effects: fatigue, diarrhoea, and changes in weight or appetite. A more recent review, by Chesney and colleagues in 2020 in Neuropsychopharmacology, ran the first meta-analysis of randomized, placebo-controlled trials on the subject. Its conclusions point the same way: compared with placebo, CBD is associated with more drowsiness, diarrhoea and appetite loss, as well as a higher rate of treatment discontinuation for side effects.
One important point: the large majority of this data comes from trials conducted at pharmaceutical quantities, often well above what an occasionally used shop flower or resin contains. That's not a reason to downplay these effects, but a benchmark worth keeping in mind when reading the figures.
Raised liver enzymes: the one genuinely serious signal
The most solid signal in the literature concerns the liver. In the trial by Devinsky and colleagues, published in 2017 in the New England Journal of Medicine on the use of cannabidiol in children with Dravet syndrome, raised liver enzymes were observed in some participants, particularly those also receiving valproate, a common anti-epileptic drug. Chesney et al.'s 2020 meta-analysis finds the same pattern across all the trials analyzed: the risk of abnormal liver test results rises markedly compared with placebo, especially at high quantities and with polymedication.
This rise is generally reversible on stopping or lowering the quantity used. It remains documented at pharmaceutical exposure levels, well above those of relaxation-oriented use. But it justifies a simple rule: anyone with a known liver condition, or taking a treatment metabolized by the liver, should talk to a doctor before using CBD.
Drug interactions: CYP3A4, CYP2C19 and the list worth knowing
CBD is metabolized by the liver via enzymes from the cytochrome P450 family, particularly CYP3A4 and CYP2C19. The problem is that these are the same enzymes that break down a very long list of common medicines. By slowing them down, CBD can raise their blood concentration, with an amplified or prolonged effect.
The best-documented cases:
- Clobazam, an anti-epileptic drug. The study by Geffrey and colleagues, published in 2015 in Epilepsia, showed that combining CBD and clobazam sharply increased the concentration of clobazam's active metabolite, requiring a dose adjustment under medical supervision.
- Anticoagulants such as warfarin, where a change in concentration directly changes bleeding risk.
- Immunosuppressants used after a transplant, whose margin between an effective dose and a toxic one is narrow.
- Certain antidepressants and anti-epileptics, also metabolized by these same enzymes.
The ANSM flagged this reality in an alert published in March 2025: mixing CBD and medicines "is never harmless." The agency recorded several dozen cases of interactions reported to poison control and pharmacovigilance centres between 2017 and 2023, and urges anyone on treatment to tell their doctor before using CBD, whatever form the product takes.
Who should abstain or seek medical advice first
Certain situations call for caution, or outright abstention:
- Pregnancy and breastfeeding. Human data are lacking, and CBD crosses the placental barrier in animals. The precautionary principle applies.
- Minors. CBD is not recommended for them, outside a supervised medical setting such as Epidyolex.
- Liver impairment. The liver is already the organ that metabolizes CBD and that shows the most documented warning signal: prior medical advice is best.
- Ongoing medication, whatever it is, because of the interaction risk via CYP3A4 and CYP2C19 detailed above.
The real risk in 2026: non-compliant products
Part of the concern around CBD doesn't come from the molecule itself, but from products that don't contain what they claim to. In June 2025, the ANSM and Anses published a notice on a notable rise in poisonings linked to products presented as CBD: several hundred cases recorded since early 2024, with symptoms ranging from simple fatigue to severe illness. The most frequent cause: synthetic cannabinoids (HHC, H4-CBD and derivatives) added without the consumer's knowledge, or a THC level above the legal limit of 0.3%. A study backed by the Mildeca and conducted by addiction monitoring centres (CEIP) in 2023 had already found that a significant share of products sold displayed a CBD level different from the one stated on the label.
That's why asking for a certificate of analysis (COA) isn't an administrative detail: it's the only way to check what a product actually contains before you use it. This requirement applies to any seller, not just for flowers or resins — see our guide to reading a COA and our checklist for spotting a fake COA before ordering online.
Driving: what CBD changes, and what it doesn't
CBD doesn't get you high and doesn't cause any altered perception. But roadside saliva screening targets THC, not CBD. The issue comes from full spectrum products, which contain traces of THC even at a level below 0.3%: in France, no threshold is tolerated behind the wheel, under Article L235-1 of the Highway Code. A positive test is therefore still possible, even with a product bought legally. The detailed mechanisms and risks are covered in our article on the saliva test and CBD and in our overview of the legal framework for CBD in France.
What to do in case of a side effect
The response depends on how severe the symptom is:
- Mild effect — drowsiness, dry mouth, mild digestive discomfort: stop use and let the effect pass. There's generally nothing else to do.
- Moderate effect — digestive trouble that lasts, marked dizziness: stop, stay hydrated, and see a pharmacist if the symptom persists beyond 48 hours.
- Severe effect — clear feeling faint, jaundice, repeated vomiting, a sign suggestive of a drug interaction: contact a poison control centre (centre antipoison) or emergency services without delay.
In every case, you can report the side effect on the official portal signalement.social-sante.gouv.fr (the French health-incident reporting service). This is the system, fed by poison control and pharmacovigilance centres, that allowed health authorities to document the rise in poisonings linked to non-compliant products.
Sources
- Organisation mondiale de la santé, Comité d'experts de la pharmacodépendance (ECDD), Cannabidiol (CBD) Critical Review Report, juin 2018.
- Iffland K., Grotenhermen F., « An Update on Safety and Side Effects of Cannabidiol: A Review of Clinical Data and Relevant Animal Studies », Cannabis and Cannabinoid Research, 2017.
- Chesney E., Oliver D., Green A. et al., « Adverse effects of cannabidiol: a systematic review and meta-analysis of randomized clinical trials », Neuropsychopharmacology, 2020.
- Devinsky O. et al., « Trial of Cannabidiol for Drug-Resistant Seizures in the Dravet Syndrome », New England Journal of Medicine, 2017.
- Geffrey A.L. et al., « Drug–drug interaction between clobazam and cannabidiol in children with refractory epilepsy », Epilepsia, 2015.
- ANSM, « Mélanger CBD et médicaments, ce n'est jamais anodin », actualité, mars 2025 — ansm.sante.fr.
- ANSM / Anses, « Augmentation des intoxications causées par des produits à base de CBD contenant d'autres substances », juin 2025 — ansm.sante.fr.
- Code de la route, article L235-1, sur la conduite après usage de stupéfiants — à vérifier sur legifrance.gouv.fr pour la version en vigueur.
