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You know the scene: It’s a Friday night, everyone’s hanging out, and someone pulls out a joint. Choosing to smoke two joints (or even just take a puff of one) is illegal in most states, but we’re not going to get into the medical marijuana debate here. We’re not even going to chat about if smoking marijuana is bad for you (hint: the results are mixed). Rather, we’re interested in how Mary Jane affects the brain. Read on for the lowdown on THC, cannabidiol, anandamide, and other hard-to-pronounce chemicals found in Jay and Silent Bob’s favorite plant.

How the Herb Works

Each little bud and leaf of the marijuana plant is composed of hundreds of chemicals, but scientists have mainly studied just two main compounds: tetrahydrocannabinol (THC) and cannabidiol (CBD).

Cannabidiol is a non-psychoactive compound, but it does contribute to making the smoker feel calm and relaxed. In fact, cannabidiol has so many rock-star qualities that scientists are trying to figure out how to turn it into a drug. Cannabidiol contains analgesic (aka pain-relieving), anti-inflammatory, and antipsychotic properties that have the potential to treat patients with schizophrenia, Parkinson’s disease, anxiety, and even cancer.

Tetrahydrocannabinol (try saying that 10 times fast!), a member of the cannabinoid chemical family, is specifically responsible for the psychological and physical side effects that occur as a result of lighting up. Smoking reefer can produce feelings of euphoria, relaxed inhibitions, fragmentary thoughts, lack of concentration, impaired memory, drowsiness, and even sudden panic or paranoia. Bud affects the bod, too: Marijuana smokers may experience physical effects like increased heart rate, red eyes, dry mouth, and increased appetite.

What Happens in the Short Term?

THC gets movin’ quickly. Within seconds, the drug hits the brain and goes to town on the brain’s cells, called neurons. To understand how this works, let’s pause for a brief biology lesson. Neurons are long, dangly cells that don’t actually touch one another. The gap between brain cells is called a synapse, and the brain uses chemicals called neurotransmitters to pass messages across these gaps — think of these chemicals as an operator on a phone call. You’ve probably heard of a few neurotransmitters, like serotonin, epinephrine, and dopamine. While most neurotransmitters are made in the glands, some man-made drugs (both legal and illegal) can mimic the same effects as natural neurotransmitters. Natural or not so much, a neurotransmitter binds to a neuron, which signals the body to do (or not do) something. When a neurotransmitter fits into the correct receptor—like a key in a lock—it chemically turns that neuron off or on.

This is where our friend THC comes in. The active chemical in marijuana mimics a natural neurotransmitter called anandamide. Anandamide is often referred to as the “bliss molecule” because of its role in boosting memory and learning, dulling pain, and stimulating the appetite Anandamide administration into the ventromedial hypothalamus stimulates appetite in rats. Jamshidi N, Taylor DA. Department of Pharmaceutical Biology and Pharmacology, Victorian College of Pharmacy, Monash University, Victoria, Australia. British Journal of Pharmacology. 2001 November; 134(6):1151-4. . Anandamide normally buddies up with dopamine, and together these neurotransmitters turn on and turn off different chemical pathways as needed.

THC may mimic anandamide, but they don't produce the exact same effects. After a person takes a hit of Mary Jane, THC binds to cannabinoid CB1 and CB2 receptors, which are located in several parts of the brain (namely, the hippocampus, cerebral cortex, cerebellum, and basal ganglia)Regulation of cannabinoid CB1 receptors in the central nervous system by chronic cannabinoids. Sim-Selley LJ. Department of Pharmacology & Toxicology, Institute for Drug & Alcohol Studies, Virginia Commonwealth University Medical College of Virginia, Richmond, VA, USA. Critical Reviews in Neurobiology. 2003; 15(2)-91-119. . These brain areas are responsible for short-term memory, coordination, learning, problem solving, and unconscious muscle movements. When THC gets its groove on in the cannabinoid receptors, it gets in the way of natural neurotransmitters (like anandamide) that need to bind to those sites to make all of the functions listed above work properly.

When THC prevents anadamide from doing its job, the delicate balance between anadamide and dopamine is thrown off. The result: We’re suddenly euphoric, off-balance, ravenous, seemingly impervious to pain, and unable to retain information. Think about the classic stoner clichés for a minute…yep, all the signs and symptoms are there.

What Happens in the Long Term?

How long THC affects the brain and stays in the body depends on many factors, including the potency of the marijuana, the smoker’s experience with the drug, how the drug is ingested (via joint, bowl, bong, vaporizer, etc), and if it’s used in conjunction with other drugs or alcohol Acute and residual effects of alcohol and marijuana, alone and in combination, on mood and performance. Chait LD, Perry JL. Department of Psychiatry, Pritzker School of Medicine, University of Chicago, IL, USA. Psychopharmacology. 1994 July; 115(3):340-9. . Immediate effects of THC kick in after a few seconds and last for an hour or two, but the chemicals can stay in the body for much longer. THC is fat-soluble, so even though it doesn’t continue to affect the brain, it can hang out in body tissues for several weeks or, in the case of habitual smokers, even monthsUrinary elimination of 11-Nor-9-carboxy-9-tetrahydrocannabinol in cannabis users during continuously monitored abstinence. Goodwin RS, Darwin WD, Chiang CN, Shih M, Li SH Huestis MA. Chemistry and Drug Metabolism Section, Intramural Research Program, National Institute of Drug Abuse, National Institutes of Health, Baltimore, MD, USA. Journal of Analytical Toxicology. 2008 October; 32(8):562-569. .

So are those wild ‘n’ crazy nights going to ruin your brain forever? Some studies have shown that frequent adolescent marijuana use—especially when use begins at a younger age—can reduce IQ by middle age. Further research argues that smoking like a chimney causes overuse of the CB1 receptors, which can lead to a sloth-like brain. But more recently, a boatload of researchers have proven that puffing the magic dragon won’t actually zap your brain cells in the long-term. Current and former marijuana use: preliminary findings of a longitudinal study of effects on IQ in young adults. Fried, P., Watkinson, B., James, D., et al. Canadian Medical Association Journal, 2002 April 2; 166(7): 887–891 Neurocognitive consequences of marihuana—a comparison with pre-drug performance. Fried, PA, Watkinson, B., and Gray, R. Department of Psychology, Carleton University. Neurotoxicology and Teratology, 2005 Mar-Apr;27(2):231-9. Epub 2004 Dec 9 Neuropsychological performance in long-term cannabis users. Pope, HG Jr., Gruber, AJ, Hudson, JI, et al. McLean Hospital, Harvard Medical School. Archives of General Psychiatry, 2001 Oct;58(10):909-15 .

But Then I Got High: The Takeaway

If you stuck through the chemistry lessons until this part, you’re probably expecting a thumbs-up or thumbs-down judgment. But, as with many biological processes, the overall effect of marijuana on brain chemistry isn’t crystal clear. For the most part, current research is disproving earlier studies that claimed that marijuana damaged the body long-term, but so far nothing’s really set in stone. Feel free to take this information on the brain’s reaction to marijuana and smoke it (or not).

Originally published April 2013. Updated June 2015.

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