How Weed Works

Now that recreational marijuana use is legal in New York state, many people who only smoked a few times in college are wondering if it might be worth trying again, while others who never touched the stuff are curious if they should give it a go now that it’s no longer a crime. Given that it has likely been a few decades since you learned about the effects of marijuana on your body in health class, we’re here with a refresher on everything that happens when you smoke or otherwise inhale weed.

The effects of cannabis on the body depend on several factors. The most important are: the type and composition of the cannabis, how it’s administered, and the particulars of the person consuming it (including level of experience and psychiatric risk factors). We are developing the Human Neuropsychopharmacology Laboratory at Zucker Hillside Hospital to directly study some of these very interactions. But for now, here’s what we know about typical recreational cannabis (2% to 12% THC and minimal CBD) that is either smoked or inhaled:

A first-time user may not feel anything after just one puff. If someone has more experience, then within a few seconds to minutes, they will feel an increased heart rate, a mental buzz or high, and sometimes sensations like tingling and hunger. If they stop after one puff, these experiences will likely be mild and gone within 30 to 60 minutes. If they continue to puff, these experiences will be stronger and last longer, sometimes to the point of discomfort. For individuals with relatively little experience, or those with psychiatric risk factors, other effects can occur, such as paranoia, perceptual disturbances, and impaired attention and memory.

When you smoke or inhale cannabis, the components (cannabinoids, including THC and CBD) enter the bloodstream via the lungs, then travel to the heart, and then the rest of the body including the brain. Peak blood levels of THC are achieved within just a few minutes, whereas peak psychoactive (actually feeling high) and cardiovascular effects occur within 5 to 15 minutes.

When cannabis reaches the brain, it activates the cannabinoid CB1 receptors and impacts the release of reward-related neurotransmitters such as dopamine and endogenous opioids. This leads to an intoxicating feeling and affects the user’s sense of touch and perception, as well as cognitive and motor functions.

Directly or indirectly, cannabis also affects the respiratory, cardiovascular, and gastrointestinal systems—though much research still needs to be done in these areas. It is unclear at this point if cannabis has any significant impact on a user’s immune function.

After a single use, THC typically leaves the bloodstream rapidly, within several hours. Though some forms of THC can remain in fatty tissue and slowly reenter the bloodstream. An infrequent user will likely show a positive urine toxicology test for at least a few days after their last significant cannabis use (meaning more than just a puff). A weekly or daily user will test positive for at least several weeks. Your hair won’t keep your secrets forever though—THC can be reliably detected in the hair of heavy users for up to 90 days.

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