Six interactions are worth memorising. Two of them are not CYP interactions at all, and almost every page that lists them gets that wrong. Clobazam, valproate, warfarin, CNS depressants, the CYP3A4 group including tacrolimus, and the one nobody warns about: what happens to a patient's other medicines when they stop smoking. Below is each mechanism, the route of administration that raises it most, and the action that belongs to a coach rather than a prescriber.
CBD inhibits several liver enzymes, most importantly CYP2C19, CYP2C9 and CYP3A4. That raises the level of some drugs that use the same enzymes. Separately, cannabis adds sedation to anything else that sedates, which is not an enzyme effect at all. And combustion induces CYP1A2, which lowers the level of certain drugs, so quitting smoking can push those drugs up without anyone changing a dose.
Oral and sublingual routes carry the highest interaction load, because they put the most CBD through the liver first. Topicals carry the least.
Search this topic and you will find pages listing thirty or forty drugs. They are padded, and the padding does real harm, because a warning that applies to everything applies to nothing. A patient handed forty flags reads none of them.
The honest list is short. It is short because the bar for inclusion should be a named mechanism with human evidence behind it, not a theoretical overlap on a metabolic pathway. Most of what gets listed is the second thing.
I also want to disarm a mistake before I make it. There are a dozen receptor systems cannabis touches: GPR55, PPAR-alpha and gamma, 5-HT1A, adenosine A2A. They explain a great deal about why a full-spectrum product behaves differently from an isolate. They do not, on current human evidence, give you a cross-medication warning you can hand a patient. The discipline is to describe the effect and refuse the interaction claim. Do not invent one.
CBD inhibits CYP2C19. Clobazam's active metabolite, norclobazam, is cleared by it. Block the enzyme and norclobazam rises roughly threefold. The patient is not more sedated because cannabis is sedating. They are more sedated because there is three times as much of their own benzodiazepine metabolite in them.
Raised most by oral or sublingual CBD. The action is a flag and a level check, requested by the prescriber, not by you.
CBD plus valproate produces additive liver stress, showing up as raised ALT and AST. This is not a CYP interaction and calling it one is the most common error on this subject. Two things that burden the liver, taken together, burden it more.
Raised by any systemic CBD at dose. The action is a flag for liver function monitoring.
CBD and THC both inhibit CYP2C9, which clears warfarin. INR rises. The evidence here is at case-report level, and I will say that plainly rather than dress it up, but warfarin has a narrow therapeutic index and a case report is enough to justify caution.
Raised most by oral routes, where first-pass metabolism is maximal. The action is a flag for closer INR monitoring.
This one is pharmacodynamic, not metabolic. CB1-mediated central nervous system depression stacks with every other CNS depressant. The sedation adds. This is the best-established item on the list and it is tagged [ESTABLISHED] in my own material for that reason.
Raised by fast, high-peak routes such as inhalation, and separately by edibles, where 11-hydroxy-THC arrives late and strong. The action is a sedation flag and a no-driving conversation.
CBD inhibits CYP3A4. For tacrolimus, reported area under the curve has risen roughly threefold. These are transplant and immunosuppression drugs where level matters enormously, and the same enzyme clears several common statins.
Raised by oral or systemic CBD. The action is a flag for drug-level monitoring.
Combustion induces CYP1A2. Not cannabis itself, the smoke. An induced enzyme clears its substrates faster, so a patient who smokes has lower levels of clozapine, olanzapine, theophylline or duloxetine than their dose would otherwise produce. Their prescriber titrated them to a stable dose while that induction was in place.
Then they quit. Or they switch to a vaporiser, or to an edible. The induction disappears over days, and those drug levels climb, with nobody having changed a single prescription.
This is the interaction I see missed most often, and it is the one where a coach adds the most value, because the coach is usually the person who knows a route change is coming. Flag it before they quit, and make sure the prescriber knows a level may move.
Any drug with a narrow therapeutic index gets flagged by default, whether or not it appears above. The reasoning is simple: small shifts in exposure matter a lot when the safety margin is small. You do not need a documented cannabis interaction to justify caution there.
The route of administration is the first safety lever, not the dose. It decides how much drug arrives, when it arrives, and how much of it meets the liver on the way in.
| Route | First-pass burden | Interaction load |
|---|---|---|
| Topical | None | Low |
| Transdermal patch | Low | Low to moderate |
| Inhaled, vaporised flower | Low | Moderate |
| Inhaled, smoked flower | Low | Moderate, plus a high flag for CYP1A2 drugs |
| Sublingual or oromucosal oil | Partial, much is swallowed | Moderate |
| Oral: swallowed oil, edibles, swallowed tincture | Maximal | High |
| Suppository or rectal | Unknown | Not characterised, its own risk tier |
So for a heavily co-medicated patient, the move is to change the route before touching the milligrams. A topical aimed at a joint spares the central nervous system and the liver entirely. That is a safety decision disguised as a product choice.
I am not a doctor, a physician, a clinician or a prescriber. I hold two Israeli Ministry of Health licences: one as a patient from 2004, and one from 2008 as the first Medical Cannabis Instructor licensed in Israel, which is a licence to educate and coach rather than to prescribe.
Everything above is education. Anything that touches a lab value, an INR, a drug level or a prescribed medicine goes to the prescriber. A coach's job on this subject is to spot the flag, name it accurately, and route it to the person licensed to act on it. That is not a limitation to apologise for. It is the reason a clinician can work with you at all.
Six are worth memorising. CBD inhibits CYP2C19 and raises clobazam's active metabolite norclobazam roughly threefold. CBD plus valproate causes additive liver stress, which is not an enzyme interaction. CBD and THC inhibit CYP2C9 and can raise INR on warfarin, at case-report level. Cannabis adds sedation to opioids, benzodiazepines, alcohol and Z-drugs, which is the best established item on the list. CBD inhibits CYP3A4 and has raised tacrolimus exposure roughly threefold, which also affects several statins. And smoking induces CYP1A2, so stopping smoking can raise levels of clozapine, olanzapine, theophylline and duloxetine with no dose change at all. Any narrow therapeutic index drug should be flagged by default.
Yes. CBD inhibits CYP2C19, CYP2C9 and CYP3A4. Inhibiting an enzyme means drugs cleared by it are cleared more slowly, so their levels rise. How much depends heavily on the route: swallowed oil and edibles put the most CBD through the liver first and carry the highest interaction load, while topicals carry almost none because very little reaches the bloodstream.
Because combustion induces the enzyme CYP1A2, and an induced enzyme clears its substrates faster. If you smoke, your levels of clozapine, olanzapine, theophylline or duloxetine are lower than your dose alone would produce, and your prescriber stabilised you while that was true. When you stop smoking, or switch to a vaporiser or an edible, the induction fades over days and those levels climb, without any prescription changing. This is the interaction most commonly missed. Tell your prescriber before you quit, not after.
The sedation adds. CB1-mediated central nervous system depression stacks with every other CNS depressant, including opioids, benzodiazepines, alcohol and Z-drugs, and this is the best evidenced interaction of the group. Fast high-peak routes such as inhalation and late-arriving edibles both matter. Treat it as a sedation and driving conversation, and have it with the prescriber who manages the other medicine.
Often yes, and it is usually the first thing to try. A topical aimed at a joint reaches peripheral CB2 and TRPV1 in the tissue while sparing the central nervous system and the liver, so it carries the lowest interaction load. A vaporised dose avoids combustion and so avoids the CYP1A2 effect. Oral routes carry the highest load because first-pass metabolism is maximal. For a patient on three or more interacting medicines, changing the route lowers the risk before the dose is touched at all.
The course that accompanies the book opens with its first module free and complete: three videos, about twenty-eight minutes, and no pharmacology at all. It is the method you then use on everything else, mine included. It is also where I say out loud that I taught a fixed twenty-eight day tolerance reset from stage for years, went looking for the study behind the number, found that it does not exist, and stopped teaching it.
No card, no call. The rest of the course is paid, and by then you will have seen exactly how I teach.
Watch module one free
Gil Luxenbourg