Cannabis Pharmacokinetics: How Cannabinoids Move Through the Body

Not medical advice

This article summarizes published pharmacokinetic data on cannabinoids. It is educational reference material, not medical advice. Individual response varies substantially with genetics, tolerance, other medications, liver function, and product formulation. Talk to a qualified clinician before using cannabis medically, especially if you take other prescription drugs — cannabinoids interact with the cytochrome P450 system and can alter blood levels of many medications Strong evidence.

Plain-language summary

Pharmacokinetics (PK) is what the body does to a drug: Absorption, Distribution, Metabolism, Excretion (ADME).

For cannabis, the practical takeaways are:

• How you take it changes almost everything. Smoking or vaping delivers THC to the brain within minutes. Eating it takes 1–3 hours and produces different metabolites ^[1][2].
• Bioavailability is low and variable. Only a fraction of the THC in a joint or gummy actually reaches your bloodstream, and the fraction differs from person to person and puff to puff ^[1][3].
• THC is very fat-soluble. It gets stored in body fat and released slowly, which is why urine tests can stay positive for weeks in heavy users ^[4].
• The liver makes THC stronger — sometimes. Oral THC is converted by the liver into 11-hydroxy-THC (11-OH-THC), which is roughly as psychoactive as THC itself and crosses into the brain readily. This is why edibles feel different from smoking ^[1][5].
• CBD is poorly absorbed orally. Most swallowed CBD never makes it to systemic circulation, and food dramatically changes how much does ^[6].

What we know well (strong evidence)

Inhalation

Smoked and vaporized THC reach peak plasma concentrations in 3–10 minutes, with subjective effects peaking within 15–30 minutes and largely subsiding within 2–4 hours ^[1][2] Strong evidence. Bioavailability ranges from about 10% to 35%, depending on depth of inhalation, breath-hold, device, and experience ^[1][3] Strong evidence. Vaporization delivers roughly similar bioavailability to smoking but avoids most combustion byproducts ^[2] Strong evidence.

Oral (edibles, capsules, oils)

Oral THC has a slow, erratic absorption curve. Peak plasma levels typically occur 1–3 hours after ingestion but can be delayed up to 6 hours, and inter-individual variability is large ^[1][5] Strong evidence. Oral bioavailability is low (~4–20%) due to extensive first-pass metabolism in the liver ^[1] Strong evidence.

Oral dosing produces much higher concentrations of the active metabolite 11-OH-THC than inhalation does. 11-OH-THC is comparably psychoactive to THC and contributes to the reputation of edibles as "stronger and weirder" ^[1][5] Strong evidence.

CBD

Oral CBD bioavailability in fasted adults is approximately 6% ^[6] Strong evidence. A high-fat meal increases CBD exposure roughly 4–5-fold ^[6][7] Strong evidence. This is a large enough effect that FDA labeling for Epidiolex (purified CBD) specifically addresses food effects ^[8].

Distribution and elimination

THC is highly lipophilic and distributes rapidly into fatty tissues. The terminal elimination half-life after a single dose is around 20–30 hours, but with chronic use, THC redistributes from fat stores and the apparent half-life extends to several days ^[1][4] Strong evidence. THC and its metabolites are excreted mostly in feces (~65%) and urine (~20%) ^[1] Strong evidence.

Drug interactions

Both THC and CBD are metabolized by cytochrome P450 enzymes (CYP3A4, CYP2C9, CYP2C19). CBD in particular inhibits several CYP enzymes and can raise levels of drugs like clobazam, warfarin, and tacrolimus ^[8][9] Strong evidence.

What we understand partially (weak or emerging evidence)

• Sublingual and oromucosal absorption. Products like nabiximols (Sativex) claim buccal absorption bypassing first-pass metabolism, but studies suggest most of the dose is actually swallowed and absorbed enterally. Real oromucosal contribution appears modest ^[10] Weak / limited.
• Topical cannabinoids reaching systemic circulation. Non-transdermal topicals produce minimal systemic THC/CBD levels. Purpose-built transdermal patches can achieve measurable plasma levels, but published PK data are limited Weak / limited.
• Rectal THC. Widely repeated claims of high rectal bioavailability trace back to a small number of studies, some using a THC hemisuccinate prodrug that is not what's in most suppository products on the market. Bioavailability of native THC via rectal route is likely low ^[11] Disputed.
• Nanoemulsions and "fast-acting" edibles. Emulsified beverages and dissolvable powders do reach peak plasma faster than oils, but the magnitude and consistency of the improvement varies by product and is often overstated in marketing Weak / limited.
• Pediatric and elderly PK. Most PK data come from healthy adults aged 18–55. Data in children (outside the Epidiolex program) and adults over 65 are thin Weak / limited.

What is folklore or unsupported

• "Edibles kick in at exactly 45 minutes." No. Onset ranges from 30 minutes to 3+ hours depending on the person, the meal, and the formulation ^[1][5] [evidence:none for the specific claim].
• "Holding smoke in longer gets you higher." Most THC absorption from a puff occurs within the first few seconds. Extended breath-holds mainly increase tar exposure and lightheadedness from hypoxia ^[2] [evidence:strong against].
• "Mango terpenes boost your high by activating myrcene." No controlled human PK study supports this Anecdote.
• "CBD has no drug interactions because it's natural." Demonstrably false — see the strong evidence section [evidence:strong against].

What we genuinely don't know

• The pharmacokinetics of minor cannabinoids (CBG, CBN, THCV, CBC) in humans are barely characterized. Most published PK is for THC, CBD, and their primary metabolites.
• How chronic heavy use reshapes tissue distribution and elimination in real-world users is inferred more than measured.
• Whether the "entourage effect" produces meaningful PK interactions between cannabinoids and terpenes at realistic doses is unresolved Disputed.
• Individual genetic variation (e.g., CYP2C9 polymorphisms) clearly affects THC metabolism, but clinically actionable dosing guidance based on genotype does not yet exist ^[9] Weak / limited.

Comparison with standard pharmaceutical PK

Compared to typical oral small-molecule drugs, cannabis is unusual in three ways:

1. High and variable first-pass metabolism. Oral THC bioavailability (~6%) is closer to a poorly-absorbed peptide than a typical small molecule.
2. An active metabolite formed disproportionately by one route. 11-OH-THC production is much higher after oral dosing, meaning route of administration changes not just kinetics but pharmacodynamics.
3. Deep tissue reservoir. Storage in fat and slow redistribution produce a long tail of detectable (though usually sub-psychoactive) drug levels, complicating drug testing and post-incident forensic interpretation ^[4] Strong evidence.

Pharmaceutical cannabinoids — dronabinol (synthetic THC), nabilone (THC analog), Epidiolex (CBD), and nabiximols (THC:CBD spray) — have characterized PK profiles used for approved dosing. Botanical flower and unregulated edibles do not, and label claims on consumer products should be treated with skepticism Strong evidence.

Risks tied to pharmacokinetics

• Overdose from edibles. Because oral onset is slow, users redose before the first dose peaks, leading to acute intoxication — a leading cause of cannabis-related ER visits in legal markets ^[12] Strong evidence.
• Drug–drug interactions. Especially with CBD at anti-epileptic doses ^[8][9] Strong evidence.
• Impaired driving windows. Inhaled THC impairs psychomotor performance for roughly 3–6 hours, but blood THC levels do not correlate well with impairment, complicating per-se DUI laws ^[13] Strong evidence.
• Prolonged positive drug tests in chronic users due to fat storage — a PK issue with employment and legal consequences, not a pharmacologic one ^[4] Strong evidence.

Sources

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