CBD interacts with a surprisingly long list of medications. It interferes with the same liver enzymes that break down many common drugs, which can cause those drugs to build up to higher-than-normal levels in your body. In a review of 53 drug substrates studied alongside CBD, 31 showed increased drug concentrations. The interactions range from mild drowsiness to dangerous toxicity, depending on the medication involved.
How CBD Interferes With Your Medications
Most medications are processed by a family of liver enzymes. CBD inhibits several of the most important ones, including CYP3A4, CYP2C19, CYP2C9, CYP2D6, and CYP1A2. These enzymes are responsible for breaking down a huge proportion of prescription and over-the-counter drugs. When CBD blocks them, the medication lingers in your bloodstream longer and reaches higher concentrations than intended.
CBD also inhibits transport proteins that control how drugs move in and out of cells. This means it can affect drug levels through multiple pathways at once, not just liver metabolism. The result is the same: your normal dose of a medication may start acting like a higher dose, increasing the risk of side effects.
Blood Thinners
The interaction between CBD and warfarin is one of the most documented and potentially dangerous. Warfarin’s effectiveness is measured by a blood test called INR, and CBD can push that number significantly higher. In a systematic review of seven case reports involving warfarin and cannabinoids, six out of seven patients showed elevated INR levels. The increases ranged from a modest 0.4-point rise to a dramatic 9.61-point spike, either of which can raise the risk of serious bleeding.
Four of those cases required warfarin dose reductions of 22% to 31% to bring clotting levels back to a safe range. If you take warfarin and start using CBD, your clotting levels need close monitoring. The same concern applies to other blood thinners processed through similar enzyme pathways.
Anti-Seizure Medications
CBD has FDA approval as a seizure medication (Epidiolex), so its interactions with other anti-seizure drugs are especially well studied. The most significant interaction is with clobazam. CBD strongly inhibits CYP2C19, the enzyme that breaks down clobazam’s active metabolite. When CBD is added, levels of that metabolite rise, leading to increased sedation and drowsiness. The FDA labeling for Epidiolex specifically recommends reducing clobazam doses when the two are used together.
Valproate is another concern. Taking CBD alongside valproate increases the risk of liver enzyme elevations, a sign of liver stress. The FDA recommends considering dose reductions of one or both drugs in this situation. Stiripentol, another anti-seizure drug, also accumulates to higher levels when taken with CBD.
Immunosuppressants
For transplant recipients or anyone on immunosuppressive therapy, CBD poses a serious risk. Tacrolimus and cyclosporine are both processed by CYP3A4, one of the main enzymes CBD blocks. In a published case report, a 32-year-old woman who had been stable on tacrolimus for a year entered a CBD clinical trial. After her CBD dose was increased to 2,000 mg per day, her tacrolimus concentrations roughly tripled. She developed signs of tacrolimus toxicity, including declining kidney function.
Other immunosuppressants processed through similar pathways, including everolimus and sirolimus, carry the same risk. The FDA labels these as drugs requiring blood level monitoring and possible dose reductions when combined with CBD.
Antidepressants and Psychiatric Medications
Many antidepressants, including common SSRIs like sertraline and fluoxetine, are broken down by the same liver enzymes CBD inhibits. When CBD slows their metabolism, drug levels can climb, potentially intensifying side effects like nausea, dizziness, or emotional blunting.
The sedation risk is compounded when CBD is combined with any psychiatric medication that already causes drowsiness. Antipsychotics, benzodiazepines like Xanax or Ativan, and sedating antidepressants can all produce amplified sleepiness, fatigue, and impaired coordination when paired with CBD. This increases the risk of falls and driving accidents.
Opioid Pain Medications
CBD’s interaction with opioids is complex. Opioids like hydrocodone, oxycodone, and morphine are metabolized through pathways CBD can influence. One case study found that cannabis altered how quickly hydrocodone was absorbed, changing the drug’s blood levels and timing. While CBD and opioids together could theoretically increase sedation risk, research specifically documenting respiratory depression from this combination is still limited.
The more immediate concern is the additive sedation effect. Both CBD and opioids cause drowsiness on their own. Combined, the effect can be stronger than either alone, which matters for anyone who needs to stay alert during the day.
Heart Medications
Several cardiovascular drugs are processed by the enzymes CBD inhibits. Digoxin, used for heart rhythm and heart failure, is a substrate of P-glycoprotein, one of the transport proteins CBD blocks. The FDA’s Epidiolex labeling specifically flags digoxin as a drug requiring monitoring when used alongside CBD.
Statins, calcium channel blockers, and antiarrhythmic drugs processed through CYP3A4 are also at risk of elevated blood levels. Because many heart medications have narrow dosing windows where too much or too little can cause problems, even modest changes in drug concentration can be clinically meaningful.
Other Medications on the FDA’s Interaction List
The FDA-approved labeling for prescription CBD identifies several additional drug categories:
- Theophylline and tizanidine (processed by CYP1A2) can accumulate to higher levels, and both have narrow safety margins where small increases matter.
- Clopidogrel, a blood-clotting drug, depends on CYP2C19 to convert it into its active form. CBD’s inhibition of that enzyme could make clopidogrel less effective rather than more potent, which is the opposite pattern from most interactions.
- CNS depressants and alcohol combined with CBD increase sedation and drowsiness risk.
- Rifampin and other strong enzyme inducers work in the opposite direction: they can make CBD itself less effective by speeding up its breakdown.
Why Dose Matters
Many of the documented interactions involve prescription-strength CBD doses of 600 mg per day or higher. The case reports with warfarin involved doses above 600 mg daily, and the tacrolimus interaction appeared at 2,000 mg per day. Over-the-counter CBD products typically contain 10 to 50 mg per serving, which is considerably less.
That doesn’t mean lower doses are risk-free. The enzyme inhibition still occurs at lower concentrations; it’s just less pronounced. For medications with narrow therapeutic windows, where small changes in blood levels can cause problems (warfarin, tacrolimus, digoxin, theophylline), even modest inhibition could matter. The risk also increases if you take CBD consistently rather than occasionally, since it can accumulate in your system over time.
The “Grapefruit Test” and Its Limits
You may have heard that if a medication carries a grapefruit warning, it likely interacts with CBD. This is a reasonable starting rule, since grapefruit and CBD both inhibit CYP3A4. But CBD’s reach is broader. It also blocks CYP2C19, CYP2D6, CYP1A2, and several transport proteins that grapefruit does not affect. So while the grapefruit comparison is useful as a quick filter, it underestimates the full range of CBD’s interactions.