Why Don’t Edibles Work for Everyone? CYP2C9 and THC

You eat a cannabis edible. Your friend feels it in 45 minutes. Two hours later, you feel nothing. You take more. Then it hits all at once — too hard, too late. Or it never does. You try again the next week, same brand, same dose, and the experience is completely different.

Edibles really are more variable than smoking or vaping, and part of that is genetic. Only part, though. This article separates what has been measured in humans from what gets asserted confidently online.

The First-Pass Effect: Why Edibles Are Different

When you smoke or vape cannabis, THC passes from your lungs almost directly into your bloodstream. Peak plasma concentrations arrive within minutes, psychotropic effects peak at roughly 15 to 30 minutes, and they taper off within 2 to 3 hours.

Edibles take a different route. THC is absorbed through your gut, enters the portal vein, and passes through your liver before reaching the rest of your body. Effects begin after a delay of about 30 to 90 minutes, reach their maximum at 2 to 3 hours, and last roughly 4 to 12 hours depending on dose.

That detour through the liver is the first-pass effect, and it is why oral THC is both inefficient and erratic. Oral bioavailability is only about 4 to 20%. Three things account for that: variable absorption, degradation of the drug in the stomach, and substantial first-pass metabolism in the liver into both active and inactive metabolites.

11-OH-THC: Active, But Not a Superdrug

The main active product of that first-pass metabolism is 11-hydroxy-THC (11-OH-THC). It is psychoactive and enters the brain readily, which is a genuine reason edibles can feel qualitatively different from smoking.

It is often claimed that 11-OH-THC is several times more potent than THC itself. The human data does not support that. When the two compounds were infused intravenously in people, they were found to be equally potent at producing the typical psychological and physiological effects of cannabis; equal doses produced equal psychoactive effects, although 11-OH-THC left the bloodstream faster. A 2024 controlled animal study found 11-OH-THC to be about 153% as active as THC on one measure and 78% as active on another — equal or somewhat greater overall — and its authors note that very little research-based evidence exists on 11-OH-THC as an individual compound.

So: active, roughly comparable to THC, and studied far less than the confident multipliers circulating online would suggest.

CYP2C9 and THC Metabolism

The enzyme that performs that 11-hydroxylation step is CYP2C9. In human liver microsomes, CYP2C9 is the major enzyme responsible for 11-hydroxylation of THC. CYP3A4 is also involved in THC metabolism, but it catalyzes different reactions — hydroxylation at other positions on the molecule, and epoxidation — rather than acting as a spare route for the same one. A systematic review of cannabinoid metabolism names CYP2C9 and CYP3A4 as the main P450 contributors to THC metabolism, and notes that clinical pharmacogenetic data support CYP2C9 as a significant one.

The key human study gave oral THC to 43 healthy volunteers and compared them by CYP2C9 genotype:

• People with two copies of CYP2C9*3, the reduced-function variant, had a median total THC exposure roughly three times higher than people with two normal-function copies, and about 70% lower exposure to the inactive breakdown product THC-COOH.
• CYP2C9*3 carriers also showed a trend toward increased sedation. The authors reported this as a trend, not an established effect.
• The CYP2C9*2 variant made no difference. THC pharmacokinetics did not differ by *2 status. This is worth stating clearly, because *2 is often lumped in with *3 as a “slow metabolizer” variant for THC. On the available evidence, the effect is specific to *3.

That is a real and reasonably clean genetic effect — resting on a single study of 43 people. It has not been replicated at the scale that would make it a clinical tool. If you are a CYP2C9 poor metabolizer, the direction of the finding suggests a given oral dose leaves more THC circulating, for longer.

What This Does Not Explain

Notice which way that finding points. Reduced CYP2C9 activity is associated with more THC exposure, not less. It offers a plausible account of “edibles hit me much harder than everyone else,” but it does not explain the opposite complaint.

There is no established genetic explanation for “edibles do nothing for me.” No published study identifies a variant that causes a null response to oral THC. The more mundane explanations are already sufficient: oral bioavailability is low and highly variable to begin with, absorption differs between people and between meals, and some of the dose is degraded in the stomach before it is ever absorbed.

If Your Edible Also Contains CBD

Many products combine THC and CBD, and CBD is handled by different enzymes. The FDA label for prescription CBD states that it is metabolized in the liver and the gut, primarily in the liver, by CYP2C19 and CYP3A4. CYP3A5 is sometimes named as a primary CBD enzyme; it is not.

Whether your genotype at those enzymes predicts how CBD affects you is a separate and much weaker question — we go through that evidence in CBD side effects and genetics. CBD is also an enzyme inhibitor, which matters if you take prescription medication; see CBD drug interactions.

What Your DNA Can Tell You

If you have raw DNA data from 23andMe, AncestryDNA, or another consumer DNA test, it can be read for your CYP2C9 genotype. That tells you which variants you carry. What it does not tell you is how a particular edible will affect you on a particular evening — dose, product consistency, food, and absorption all sit between a genotype and the experience, and the underlying human evidence is one 43-person study.

Decode's cannabis & CBD results report CYP2C9, CYP2C19, and CYP3A5 genotypes and their metabolizer phenotypes. You can preview the results to see exactly what is included.