When you smoke, eat, or otherwise consume weed, THC (the main psychoactive compound) enters your bloodstream and then spreads throughout your body, with a strong preference for fatty tissues where it can linger for weeks. The exact route it takes depends on how you consume it, and each method delivers THC to your brain at different speeds and in different amounts.
Inhalation: The Fastest Route
Smoking or vaping is the quickest way THC reaches your blood. When you inhale cannabis smoke or vapor, THC passes through the thin walls of the tiny air sacs in your lungs and directly into the surrounding blood vessels. From there, THC-rich blood travels straight to your heart and gets pumped to your brain and the rest of your body. Blood levels peak within 6 to 10 minutes after inhalation.
This route is relatively efficient. About 30% of the THC you inhale actually makes it into your bloodstream. The rest is lost to combustion, exhaled vapor, or gets trapped in lung tissue. Because inhaled THC goes directly from lungs to blood to brain, it bypasses the liver entirely on its first pass through the body, which is why the effects hit so quickly.
Edibles: A Slower, Stronger Pathway
When you eat a cannabis edible, THC takes a completely different path. It travels through your stomach and into your small intestine, where it gets absorbed into blood vessels that feed directly into the liver. This is where things get interesting.
Your liver converts THC into a different compound called 11-hydroxy-THC. This metabolite is slightly more potent than THC itself and crosses into the brain more easily. That’s a big reason why edible highs often feel more intense than smoking, even at similar doses. The tradeoff is speed and efficiency: only 4% to 12% of the THC in an edible actually reaches your bloodstream, and the effects can take 30 minutes to two hours to kick in because the compound has to work through your entire digestive tract first.
Other Ways THC Enters Your Body
Sublingual products (tinctures or strips placed under the tongue) let THC absorb through the thin tissue in your mouth and partially bypass the liver, similar to inhalation. This makes them faster-acting than edibles but generally slower than smoking.
Topical creams and patches work differently. THC penetrates the outer layers of skin and concentrates around hair follicles, slowly seeping into deeper tissue. Research on transdermal patches shows they can maintain a steady level of THC in the blood for about 24 hours, but standard topical creams rarely deliver enough THC into the bloodstream to produce a high. They’re mainly used for localized relief.
How THC Reaches Your Brain
THC is highly fat-soluble, which is the key to almost everything about how it moves through your body. Your brain is rich in blood vessels and fatty tissue, so THC gets there quickly and in high concentrations. Once it arrives, it slips across the blood-brain barrier (the brain’s protective filter) with relative ease, again because of its fat-soluble nature.
Inside the brain, THC locks onto CB1 receptors, which sit on the surface of nerve cells. These receptors are part of a natural signaling system your body already uses. When THC activates them, it alters the release of chemical messengers between neurons, producing the familiar effects: altered perception, relaxation, euphoria, impaired short-term memory, and changes in appetite. The receptors are concentrated in areas that control mood, memory, coordination, and pain perception, which is why weed affects all of those functions simultaneously.
Why THC Sticks Around in Fat
After the initial rush to the brain and other organs, THC redistributes into your body’s fat stores. It binds to the fat molecules (triglycerides) inside fat cells and essentially gets locked away. Under normal conditions, THC slowly diffuses back out of fat and into the bloodstream over days or weeks.
This is why weed stays detectable long after you feel sober. When your body breaks down stored fat for energy, the THC bound to those fat molecules gets released back into circulation. Research has even shown that food deprivation and stress hormones can speed up fat breakdown and temporarily bump THC blood levels back up, a phenomenon sometimes called “reintoxication.” People with more body fat may store more THC overall, though research on this is still limited because most studies have involved leaner participants.
How Your Liver Breaks THC Down
Your liver does the heavy lifting when it comes to clearing THC from your system. A specific enzyme called CYP2C9 handles roughly 70% of THC processing. It first converts THC into the active metabolite (11-hydroxy-THC), then breaks that down further into an inactive compound called THC-COOH. This inactive leftover is what most drug tests actually detect.
Genetics play a real role in how fast this happens. Some people carry a variant of the CYP2C9 gene that retains only about 7% of normal enzyme activity. For those individuals, a single oral dose of THC produces roughly three times the blood exposure compared to someone with the standard version of the gene. In practical terms, they get higher for longer from the same dose. When this primary enzyme is sluggish, backup enzymes (CYP3A and CYP2C19) pick up some of the slack, but the overall clearance is still slower.
How THC Leaves Your Body
Your body eliminates about 80% to 90% of a THC dose within five days, according to CDC data. The breakdown is roughly 65% through feces and 20% through urine, with the remainder accounted for by sweat, hair, and other minor routes. The compounds exiting in urine are almost entirely inactive metabolites, not THC itself.
For occasional users, blood THC levels typically drop to around 2 nanograms per milliliter within four to six hours of smoking. But chronic users accumulate so much THC in their fat tissue that it can remain detectable in blood for up to a month and in urine for up to three months. The slow, steady leak from fat stores keeps feeding metabolites back into the bloodstream long after the last use, which is why heavy users face much longer detection windows on drug tests than someone who tried it once.