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An Expert Explains What Happens To Your Body When You Smoke Weed

It’s not just bloodshot eyes and munchies.

Whether you’re an avid stoner or never touched a joint in your life, chances are you’re familiar with the things that happen when you smoke weed. The drowsiness, the giggles, the sudden deep desire to discuss eighth grade philosophy, and other such overt symptoms are all the result of hidden processes going on in your body when you get high.

You probably have at least a vague understanding of how weed works: The chemical tetrahydrocannabinol, better known as THC, zips through your bloodstream after ingestion and interacts with parts of your brain like the hippocampus and orbitofrontal cortex to cause a high. It’s more complicated than that, of course, but the general concept isn’t difficult to grasp (unless you’ve had one too many pot brownies).

“The effects of marijuana depend in part on the strain of marijuana and whether the person is a chronic user or not,” Dr. Keith Heinzerling M.D., addiction medicine specialist at Providence Saint John’s Health Center, tells Bustle. A giant hit of a high-THC strain will affect you very differently than if you have a tiny nibble on a pot cookie.

But what causes the red eyes? Why do some people experience cotton mouth or find it affects their sex life? Perhaps most importantly, what’s the deal with the munchies? Fortunately for the curious — or those who prefer to know what’s going on inside their bodies — there’s plenty of research devoted to answering these questions.

1. Dopamine Floods Your Brain

Like most drugs, cannabis’s high comes from the neurotransmitter dopamine, which is associated with our brain’s reward system; as noted by a study in the National Institute of Drug Abuse, dopamine is responsible for “pleasure, memory, thinking, concentration, movement, coordination, and sensory and time perception.”

“THC acts through cannabinoid receptors in the brain and body,” Heinzerling says. Using these receptors, THC stimulates the release of dopamine in large amounts, causing feelings of euphoria. It’s this reaction that’s responsible for the “high” you feel after using cannabis. Heinzerling adds that dopamine isn’t the only thing that’s affected by weed; it also alters other receptors for neurotransmitters like GABA and serotonin, which influence your mood. Your particular flavor of high depends on which neurotransmitters are impacted.

2. Body Fluids Dry Up

Talk about a mood killer. A study published in Journal Of Sexual Medicine in 2010 found that weed can temporarily dry up mucus membranes throughout your body, including your vagina — hence the term “cotton vagina” that’s been, well, cottoning on in some circles. Other mucus membranes in your body include your eyes and mouth, so you may feel dryness effects in those regions too, depending on the strain of cannabis and your individual reactions to them.

3. Your Blood Pressure Drops

Weed causes blood vessels across your body to dilate, creating a drop in blood pressure. This is most apparent in your eyes; as your blood vessels expand, they appear red, and your pupils may become dilated — this is what gives people the “bloodshot” look in their eyes after using cannabis. Simultaneously, breathing passages relax and open up, which contributes to the feeling of relaxation and calm that some people experience during a high.

4. Your Senses Get More Intense

You might notice that in addition to the depressive effects of a slower heart rate and the widening of your breathing passages, your senses also seem more acute — you may notice different smells, touches, or other sensations that you might not normally note, or experience them in more intense degrees.

This is because, in addition to triggering the release of dopamine, THC binds to brain receptors associated with your senses of smell and taste, which has been shown to heighten their sensitivity. Combined with the side effect of pupil dilation, many of your senses can become temporarily heightened. This is the reason that THC affects your cognition and coordination when you’re very high, Keinzrling says – and it’s why driving while stoned is a bad idea.

5. Your Heart Rate Increases

Despite the fact that weed is used for many as a relaxant, what you may not realize is that smoking weed is known to speed up your heart rate for up to three hours after getting high; the dilation of your blood vessels causes the muscles in your heart to work harder to pump blood. Heinzerling says THC can also heighten your risk of anxiety and panic attacks, which make the heart pound rapidly. Although a quick heart rate is often harmless, the National Institute on Drug Abuse notes that a racing heart rate can increase your chances of having a heart attack, especially when combined with the drop in blood pressure.

6. Your Sense Of Hunger Is Distorted

Even if you don’t smoke, you’re no doubt familiar with the munchies. Researchers (and stoners) have long known that cannabis increases appetite, and recently, science has begun to shed light on the reason. “THC is responsible for most of the psychoactive effects associated with cannabis use including the high as well as increased appetite (“munchies”),” Heinzerling says. According to a 2015 study published in Nature Neuroscience, THC “flips a switch,” so to speak, on the neurons that were previously responsible for telling your body to stop eating. When you get high, these neurons begin signaling that you’re actually starving — and suddenly you find yourself in the Taco Bell parking lot surrounded by what used to be seven burritos.

Readers should note that laws governing cannabis, hemp and CBD are evolving, as is information about the efficacy and safety of those substances. As such, the information contained in this post should not be construed as legal or medical advice. Always consult your physician prior to trying any substance or supplement.

Keith Heinzerling M.D.

Crean, R. D., Crane, N. A., & Mason, B. J. (2011). An evidence based review of acute and long-term effects of cannabis use on executive cognitive functions. Journal of addiction medicine, 5(1), 1–8. https://doi.org/10.1097/ADM.0b013e31820c23fa

Koch, M., Varela, L., Kim, J. et al. (2015) Hypothalamic POMC neurons promote cannabinoid-induced feeding. Nature519, 45–50. https://doi.org/10.1038/nature14260

Prashad, S., & Filbey, F. M. (2017). Cognitive motor deficits in cannabis users. Current opinion in behavioral sciences, 13, 1–7. https://doi.org/10.1016/j.cobeha.2016.07.001

Smith, A. M., Ferris, J. A., Simpson, J. M., Shelley, J., Pitts, M. K., & Richters, J. (2010). Cannabis use and sexual health. The journal of sexual medicine, 7(2 Pt 1), 787–793. https://doi.org/10.1111/j.1743-6109.2009.01453.x

Winton-Brown, T. T., Allen, P., Bhattacharyya, S., Borgwardt, S. J., Fusar-Poli, P., Crippa, J. A., Seal, M. L., Martin-Santos, R., Ffytche, D., Zuardi, A. W., Atakan, Z., & McGuire, P. K. (2011). Modulation of auditory and visual processing by delta-9-tetrahydrocannabinol and cannabidiol: an FMRI study. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 36(7), 1340–1348. https://doi.org/10.1038/npp.2011.17

This article was originally published on Feb. 11, 2016

Whether you’re an avid stoner or never touched cannabis in your life, chances are you’re familiar with the things that happen when you smoke weed.