The FDA says research on CBD combined with herbs and other plant-based supplement ingredients is limited and advises caution. NIH sources flag individual herbs for sedation, liver injury or drug interactions, but we found no human study of those herbs with THC or CBD. Treat the combination as a question for a pharmacist.
If you use cannabis or CBD and also take herbal supplements or sleep teas, you are combining things that very little research has examined together. That does not mean the combination is dangerous, and it does not mean it is safe. It means the honest answer to "can I take this with that?" is usually "ask a pharmacist who can see your whole list." This guide covers what the FDA and NIH sources say, which herbs carry flags worth knowing about, and what to bring to that conversation.
What the FDA says about CBD and herbs
The FDA's consumer update on cannabis-derived products (content current as of March 5, 2020) lists how CBD interacts with herbs and other plant materials among the questions it cannot yet answer. It says research on CBD combined with herbs and other plant-based ingredients in dietary supplements is limited, and it advises caution when combining CBD products with herbs or dietary supplements.
The same update says CBD can affect how other drugs you take work, that using CBD with alcohol or other drugs that slow brain activity raises the risk of sedation and drowsiness, and that CBD can cause liver injury. Our cannabis medication interaction checklist covers those points for prescription medicines.
What published reviews add, and what they do not
A 2014 systematic review in Drug Metabolism Reviews identified CYP2C9 and CYP3A4 as significant contributors to the metabolism of THC, and CYP2C19 and CYP3A4 for CBD. Those are liver enzymes that also process many medicines. The authors concluded that enzyme inhibition and induction studies generally suggest a low risk of clinically significant interactions with most use, and noted that specific human data were lacking.
A 2024 systematic review in Frontiers in Pharmacology looked at real-world reports instead. It found 31 reports of altered drug levels or adverse events involving 16 narrow-therapeutic-index prescription drugs, with warfarin, valproate, tacrolimus and sirolimus reported most often. The authors concluded that interactions are likely among prescription drugs that share common CYP450 pathways, and they recommended open communication between patients and clinicians about cannabis use.
Both reviews are about prescription drugs, not herbs. We did not find a human study that tested any of the herbs below together with THC or CBD. A missing study is not evidence of safety. It means the risk cannot be measured, which is the reason to ask.
Three ways a combination could matter
The following is our own framing of the overlaps the sources point to. Each one is a reason to ask a question, not a finding that a combination causes harm.
- Added sedation. THC can cause drowsiness (see our interaction checklist), and the FDA warns about CBD with other drugs that slow brain activity. NCCIH describes theoretical reasons that chamomile and lavender might interact with sedatives and lists sedatives among ashwagandha's possible interactions. Sedation from two sources could add up, but no study measured it for these pairings.
- Liver strain. The FDA says CBD can cause liver injury. NCCIH reports rare cases of liver injury linked to kava, some serious or fatal, and a number of cases linked to ashwagandha supplements. How those risks combine is unknown.
- Changes in drug levels. NCCIH describes St. John's wort as a strong inducer of liver enzymes with documented interactions with several medicines. THC and CBD are processed by some of the same enzymes. The sources we reviewed show the St. John's wort effect for other medicines, not for THC or CBD, so for cannabinoids it remains a question.
Herbs that come up most, and what the sources flag
| Herb | Why it comes up | What NIH sources flag |
|---|---|---|
| St. John's wort | Sold for mood | NCCIH rates its overall interaction risk as high. Documented interactions include cyclosporine, indinavir, oral contraceptives, warfarin, digoxin and benzodiazepines, and certain antidepressants can cause serotonin-related effects. |
| Kava | Used for relaxation and anxiety | Rare liver injury cases, some serious or fatal. Drinking kava with alcohol is listed among possible contributors. No source we reviewed addressed kava with cannabis or CBD. |
| Ashwagandha | Stress and sleep | Possible interactions with medicines for diabetes and high blood pressure, immunosuppressants, sedatives, anti-seizure medicines and thyroid hormone medicines. A number of liver injury cases. Avoid in pregnancy and breastfeeding. |
| Chamomile | Sleep tea | Reported interactions with warfarin and some liver-processed drugs. In theory, interactions with sedatives. Allergic reactions, especially in people allergic to ragweed. |
| Lavender | Calm and sleep | Theoretical interactions with some sedative drugs or herbs, which matters before surgery. Allergic skin reactions with topical use. |
NCCIH cautions that many herb and drug interactions are theoretical, inferred from animal or laboratory studies rather than confirmed in people. It still says concern is warranted for drugs with a narrow safety margin, such as warfarin and digoxin. Our guide to herbs for sleep and stress covers the evidence for chamomile, lavender and ashwagandha in detail.
Who should be especially careful
- Anyone on a narrow-margin medicine. Warfarin and digoxin are the examples NCCIH raises for herbs, and warfarin is one of the drugs most often reported with cannabinoids.
- Anyone with liver disease or a history of liver problems. The FDA and NCCIH both report liver injury linked to some of these products.
- Anyone pregnant, breastfeeding or trying to conceive. NCCIH says little is known about chamomile and lavender in pregnancy and breastfeeding, and it advises avoiding ashwagandha.
- Anyone with a thyroid or autoimmune condition. NCCIH does not recommend ashwagandha in those cases.
- Anyone with surgery coming up. NCCIH says some supplements can change bleeding or the response to anesthesia, and advises telling your providers as early as possible.
What to bring to a pharmacist
- Every cannabis or CBD product, with THC and CBD in milligrams per serving, how you take it and when.
- Every supplement, with the Latin name, plant part and milligrams per serving, or a photo of the Supplement Facts panel.
- Teas, including how many cups a day. Herbal teas count.
- Prescription and over-the-counter medicines, and how much alcohol you drink.
- Any new drowsiness, dizziness, nausea, bruising, mood change or other symptom since you started something new.
Three questions to ask: Does anything on this list change how my medicines are processed? Could any of it add to sedation? Is there a reason to stop something before a procedure? The authors of the 2024 review also released a free online tool, CANN-DIR, to help identify potential interactions with cannabinoids.
If something goes wrong
NCCIH advises that if you have side effects from a supplement, you stop taking it and contact your health care provider. Consumers can also report safety concerns to the U.S. Department of Health and Human Services Safety Reporting Portal. Do not stop a prescription medicine on your own to make room for a supplement or a cannabis product.
Where this fits on CannaWize
CannaWize lists herbal products from a retail partner with their lab-evidence status stated plainly, and we earn a commission on purchases made through those links. That does not change what we report about interactions. We are not recommending that anyone combine herbs with cannabis. Browse herbal supplements, read our supplement buying checklist, and use our retailer profile to see which claims we verified.
Frequently asked questions
Can I take herbal supplements while using CBD?
The FDA says research on CBD combined with herbs and other plant-based supplement ingredients is limited and advises caution when combining them. That is neither a finding of harm nor a finding of safety. A pharmacist who can see your full list is the right person to ask. Source: FDA.
Is it safe to combine kava with cannabis?
We did not find a study of kava with cannabis or CBD. NCCIH links kava to rare liver injury, some of it serious or fatal, and lists drinking kava with alcohol among possible contributors. The FDA says CBD can cause liver injury. Whether the two add together is unknown, so it is a question for a clinician. Sources: NCCIH and FDA.
Does St. John's wort interact with CBD or THC?
NCCIH says St. John's wort strongly induces liver enzymes and has documented interactions with medicines including warfarin and benzodiazepines. A 2014 systematic review found that THC and CBD are processed by some of the same enzymes, including CYP3A4. We did not find a human study of St. John's wort with THC or CBD, so the effect on cannabinoid levels is unknown. Sources: NCCIH and PubMed.
What should I tell my pharmacist about cannabis and supplements?
Bring every cannabis or CBD product with its THC and CBD milligrams per serving, every supplement with its Latin name and amount per serving, any herbal teas, your prescription and over-the-counter medicines, and how much alcohol you drink. Tell them about any upcoming surgery. NCCIH advises telling your providers about every supplement you take. Source: NCCIH.
Sources and further reading
- FDA: What to Know About Products Containing Cannabis or Cannabis-Derived Compounds, Including CBD
- NCCIH: Herb-Drug Interactions, What the Science Says
- NCCIH: Kava, Usefulness and Safety
- NCCIH: Ashwagandha
- NCCIH: Chamomile
- NCCIH: Lavender
- NCCIH: Sleep Disorders and Complementary Health Approaches, Usefulness and Safety
- NCCIH: Using Dietary Supplements Wisely
- Stout and Cimino, Drug Metabolism Reviews 2014: Exogenous cannabinoids as substrates, inhibitors, and inducers of human drug metabolizing enzymes, a systematic review
- Nachnani et al., Frontiers in Pharmacology 2024: Systematic review of drug-drug interactions of delta-9-tetrahydrocannabinol, cannabidiol, and Cannabis