Cannabis Half-Life: How Long Does Weed Stay in Your System?

Cannabis stays in your body much longer than the high lasts. The plasma half-life of delta-9 THC is roughly 1.5 to 4 hours, while its main metabolite, carboxy-THC, has a half-life of about 3 to 13 days. That gap explains why a urine test can read positive for 3 days after one use and up to 30 days in daily, long-term users.

how does body fat affect cannabis half life

What Does Half-Life Mean for Cannabis?

Half-life is the time your body takes to clear half of a substance from the bloodstream. THC leaves blood quickly because it is fat-soluble and shifts into fatty tissue, then leaks back out slowly. Each half-life cuts the remaining amount in half, so a compound with a 13-day half-life can linger for weeks.

Cannabis Half-Life and Clearance Time: What to Know Before You Buy

What Is the Half-Life of THC and Its Metabolites?

• Delta-9 THC: plasma elimination half-life of about 1.5 to 4 hours, with a terminal half-life near 25 hours.
• 11-OH-THC: active metabolite with a similar short half-life.
• Carboxy-THC (THC-COOH): about 3 to 13 days, and longer in chronic heavy users.

How Long Does Weed Stay in Your System by Test Type?

Urine

Single use: up to 3 days. Moderate use: 3 to 7 days. Heavy daily use: 10 to 30 days or more. Urine tests look for carboxy-THC, the slow-clearing metabolite.

cannabis half life in blood vs urine

Blood

THC is usually detectable in blood for 3 to 12 hours, and carboxy-THC for up to 36 hours or a few days after heavy use. Blood tests reflect recent use more than past weeks.

Saliva

Oral fluid tests typically detect THC for 1 to 3 days, often up to 48 hours. They are common in roadside and workplace screening programs.

Hair

Hair tests can show cannabis use for up to 90 days because metabolites deposit in the follicle as hair grows. They cannot show same-day use.

What Changes How Long Cannabis Stays in Your System?

• Frequency and dose: daily high-dose users clear THC more slowly.
• Body fat percentage: THC stores in fat and releases over time.
• Metabolism, age, liver function, and genetics.
• Hydration, exercise, and diet have small, temporary effects.
• Concentrates, edibles, and high-potency products raise total intake.

Can You Detox THC Faster?

No supplement or drink has been proven to clear THC faster. Time is the main factor, and hydration plus regular activity support normal elimination. A test can still detect metabolites long after you feel sober.

Does Half-Life Predict a Negative Test?

No. Half-life describes blood clearance, not test cutoffs. A test can stay positive well past the half-life math because carboxy-THC sits in fat and collects in urine.