Why Medical Marijuana Affects Everyone Differently: Genetics, Enzymes, and Your Endocannabinoid System

You've probably noticed it: two people take the same medical marijuana product, same dose, same route of administration — and have completely different experiences. One gets effective pain relief with mild relaxation. The other gets anxious, dizzy, and no meaningful symptom improvement.

This isn't random. It's pharmacogenomics — the study of how your genetic makeup influences your response to medications. And medical marijuana may be one of the most genetically variable therapeutic agents in modern medicine.

Understanding why your body responds the way it does to medical marijuana isn't just academic. It has practical implications for dosing, product selection, and whether you'll benefit from medical marijuana at all.

Your Liver: Where THC Becomes Something Else

When you ingest THC — through edibles, capsules, or tinctures — it passes through your liver before reaching systemic circulation. This "first-pass metabolism" converts delta-9-THC into 11-hydroxy-THC (11-OH-THC), a metabolite that is 2-4 times more potent at CB1 receptors than the parent compound. This is why edibles often feel stronger and different from inhaled medical marijuana.

The liver enzymes responsible for this conversion are cytochrome P450 enzymes, primarily:

• CYP2C9: The dominant enzyme for THC metabolism
• CYP3A4: A secondary pathway
• CYP2C19: Minor contributor

Here's where genetics enters: these enzymes come in different variants (polymorphisms), and the variant you carry dramatically affects how fast or slow you metabolize THC.

CYP2C9: The Gene That Matters Most

CYP2C9 has several well-characterized variants:

CYP2C9\*1 (wild type): Normal metabolizer. This is the most common variant. You process THC at the "expected" rate.

CYP2C9\*2: Reduced function. Carriers metabolize THC approximately 30% slower than wild-type. This means THC stays active in your system longer, producing extended effects from the same dose.

CYP2C9\3: Significantly reduced function. This variant reduces THC metabolism by approximately 60-70%. A 2020 study by Sachse-Seeboth et al. in Clinical Pharmacology & Therapeutics found that CYP2C9\3 homozygotes had dramatically higher THC blood levels and experienced significantly more intense effects compared to wild-type individuals given the same dose.

Population frequencies vary:

• CYP2C9\1/\1 (normal): ~65% of Caucasians, ~95% of East Asians, ~85% of African Americans
• CYP2C9\*2 carriers: ~20% of Caucasians, rare in East Asian populations
• CYP2C9\*3 carriers: ~10-15% of Caucasians, ~5% of African Americans, ~3% of East Asians

What this means practically: If you're a CYP2C9\*3 carrier, a 10 mg THC edible might hit you like 25-30 mg hits someone with wild-type metabolism. You're not being "dramatic" — your liver is genuinely processing the compound differently.

CYP2C9 and CBD Interaction

CBD is a potent inhibitor of CYP2C9. This creates a compounding effect: if you already carry a slow-metabolizer variant and you're taking a product with both THC and CBD, the CBD further inhibits your already-sluggish THC metabolism. The result can be unexpectedly intense or prolonged THC effects.

This is clinically relevant. Patients using high-CBD, moderate-THC products — often recommended as "gentler" — may paradoxically experience stronger THC effects if they carry CYP2C9 slow-metabolizer variants.

Your Endocannabinoid System: Wired Differently from Birth

Beyond metabolism, genetic variation in your endocannabinoid system itself shapes your baseline cannabinoid tone and your response to exogenous cannabinoids.

CNR1: The CB1 Receptor Gene

The CB1 receptor — the primary target for THC in the brain — is encoded by the CNR1 gene. Several polymorphisms have been identified:

rs1049353 (1359 G/A): The A allele has been associated with altered CB1 receptor expression and function. Studies have linked this variant to differences in:

• Susceptibility to cannabis dependence (Hartman et al., 2009, Pharmacogenomics Journal)
• Anxiety response to THC
• Analgesic response to cannabinoids
• Risk of metabolic syndrome (which involves the endocannabinoid system)

rs806379: Associated with differences in reward sensitivity and the subjective "pleasurable" effects of cannabinoids. Individuals with certain variants may find medical marijuana more or less reinforcing, which has implications for both therapeutic efficacy and dependence risk.

FAAH: The Enzyme That Breaks Down Your Own Cannabinoids

Fatty acid amide hydrolase (FAAH) is the primary enzyme responsible for degrading anandamide — your body's main endogenous cannabinoid. The FAAH gene has a well-studied polymorphism:

rs324420 (C385A): The A allele produces a less stable FAAH enzyme that breaks down more quickly. This means people carrying this variant have naturally higher anandamide levels throughout their bodies.

About 20% of the population carries at least one copy of the A allele. These individuals tend to:

• Report lower baseline anxiety (Dincheva et al., 2015, Nature Communications)
• Have enhanced fear extinction (relevant to PTSD treatment)
• Show reduced stress reactivity
• Potentially need less exogenous THC because their endocannabinoid tone is already elevated

The FAAH A allele has been called the "bliss gene" in popular science coverage, though this oversimplifies a complex picture. What's clinically relevant is that someone with naturally high anandamide levels may respond differently to medical marijuana than someone with low baseline endocannabinoid tone. The latter group might benefit more dramatically from supplementing their endocannabinoid system with phytocannabinoids.

COMT: The Anxiety Connection

Catechol-O-methyltransferase (COMT) is an enzyme that breaks down dopamine, norepinephrine, and epinephrine. The Val158Met polymorphism affects enzyme activity:

• Val/Val (GG): High COMT activity, rapid dopamine degradation, lower prefrontal dopamine levels
• Met/Met (AA): Low COMT activity, slower dopamine degradation, higher prefrontal dopamine levels
• Val/Met: Intermediate

A 2016 study in Translational Psychiatry by Morgan et al. found that the COMT Val158Met variant significantly modulated the cognitive and psychotic-like effects of THC. Met/Met carriers were more susceptible to THC-induced paranoia and cognitive impairment compared to Val/Val carriers.

This has direct clinical implications: if you've tried medical marijuana and experienced significant paranoia or cognitive disruption, your COMT genotype — not your character or mental toughness — may be a contributing factor.

The AKT1 Gene and Psychosis Risk

One of the most important pharmacogenomic findings in cannabinoid medicine involves the AKT1 gene. AKT1 encodes a protein kinase involved in dopamine signaling.

A landmark study by Di Forti et al. (2012) in Biological Psychiatry found that carriers of the AKT1 rs2494732 C/C genotype who used cannabis had a dramatically elevated risk of psychotic experiences compared to T/T carriers. The C/C genotype is present in approximately 25% of the population.

This doesn't mean that 25% of people who use medical marijuana will develop psychosis. The absolute risk remains low for most individuals, and medical marijuana patients using controlled doses of standardized products have a very different risk profile from heavy recreational users of high-potency products. But it does mean that genetic screening could theoretically identify individuals who should be more cautious with THC-dominant products or who might benefit from CBD-dominant alternatives.

Terpene Sensitivity and Olfactory Receptor Genetics

This is a newer and less established area, but worth mentioning. Terpenes — the aromatic compounds in medical marijuana (myrcene, limonene, linalool, beta-caryophyllene, etc.) — contribute to the "entourage effect" and may have independent therapeutic properties.

Your olfactory receptor genes influence how you perceive and potentially respond to different terpene profiles. Humans have approximately 400 functional olfactory receptor genes with enormous inter-individual variability. Some people are highly sensitive to myrcene's sedative effects; others barely notice them.

Beta-caryophyllene is particularly interesting because it's a dietary cannabinoid — it directly activates CB2 receptors. Genetic variation in CB2 receptor expression (encoded by CNR2) could modulate your response to caryophyllene-rich medical marijuana strains.

What This Means for Your Medical Marijuana Treatment

Pharmacogenomic testing for medical marijuana response isn't standard practice yet. Commercial genetic tests can identify your CYP2C9 status (this is already done for other medications like warfarin), and some direct-to-consumer genetic services report on COMT and FAAH variants. But integrating this information into medical marijuana dosing isn't yet routine.

In the absence of genetic testing, you can use your own response patterns as a guide:

You may be a slow metabolizer (CYP2C9 variant) if:

• Edibles hit you much harder than expected
• Effects from oral medical marijuana last longer than 6-8 hours
• You need significantly lower doses than "typical" recommendations
• You've had overwhelming experiences from doses others find mild

You may have high endocannabinoid tone (FAAH variant) if:

• You generally have low anxiety at baseline
• You don't feel dramatically different on low doses of medical marijuana
• You recover quickly from stressful situations
• Medical marijuana feels "subtle" even at moderate doses

You may be a COMT Met/Met carrier if:

• THC tends to make you paranoid or cognitively foggy
• You're naturally anxious even without cannabis
• You're more sensitive to caffeine and other stimulants
• CBD-dominant products work better for you than THC-dominant ones

At CORAL, Dr. Kim takes a personalized approach to medical marijuana certification and dosing guidance. While genetic testing isn't currently part of the standard evaluation, understanding that people are biologically different — not just psychologically different — in how they respond to medical marijuana is foundational to good clinical practice.

Your "ideal" medical marijuana product, dose, and schedule aren't the same as anyone else's. That's not a flaw in medical marijuana — it's a reality of human pharmacogenomic diversity.

Ready to find your personalized approach to medical marijuana? [Start your evaluation at coral.clinic/start](https://coral.clinic/start).