Whether you use it yourself, have a friend who does, or know someone who moved to Colorado for not-so-secret reasons, you probably have an opinion about weed. Marijuana is no longer a taboo stoner drug reserved for hippies.

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Cannabis (the proper name for weed) has been used as medicine for millennia. But as aspirins and opioids rose in popularity, weed use declined, and the drug was officially criminalized in 1937—against the advice of the American Medical Association.

But we're not here to debate the pros and cons of legalization. Instead, we’re interested in breaking down exactly what happens in your brain and body when you're high.

How the Plant Works

Weed and the Brain
You typically hear about two types of marijuana: C. sativa and C. indica. Scientists can’t completely agree on whether those are the only two species. Some think there’s a third or that all species are descendants of sativa. Regardless, they work the same way (up to a point).

Marijuana plants produce chemical compounds called cannabinoids. The ones that get the most attention are delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). “THC is the most psychoactive compound,” says Thorsten Rudroff, Ph.D., an assistant professor at Colorado State University who studies cannabis use in patients with multiple sclerosis. “So when you smoke cannabis, THC gives you the high feeling. The more THC you have, the more powerful the high."

“You’re more sensitive to sound; you’re hungrier,” says Beatriz Carlini, Ph.D., an associate professor at the University of Washington. “All those different sensations that people who use marijuana recreationally describe—like being more relaxed—are because of the THC.”

THC also increases dopamine levels, creating that sense of euphoria.

CBD, on the other hand, acts as an antagonist to THC, Rudroff says. Basically, it does the opposite. “CBD does not have psychoactive effects, but it does have beneficial effects,” he says. “It reduces pain and muscle spasticity, and can make you more relaxed. This is the compound of greatest interest for medical marijuana.”

It’s easy to see why researchers like Rudroff get excited about CBD, but as far as they know right now, you can’t reap the benefits of one without the other.

“You can look at this and say, ‘THC is bad, and CBD is good,’ but it's not that simple,” Rudroff says. “There are some interactions. You need both in the product to work together.” Scientists are still working out the perfect ratio for patients, but Rudroff says some research suggests it might be 1:1.

What It Does to Your Brain

First, a quick neuroscience lesson: Your brain is made up of neurons and neural circuits. Neurons are long, dangly cells that like to keep their distance from each other. To bridge the gap (or synapse), chemicals called neurotransmitters deliver messages by traveling from one neuron to another and attaching onto molecules called receptors. And guess what? There's a special kind of neurotransmitter called an endocannabinoid. Yep, your body makes its own version of weed (sort of).

“When we experience pain, inflammation, or stress—or have issues related to fear or mood—our body releases [endocannabinoids], which go to our endocannabinoid system and help get rid of those unwanted sensations,” Carlini says.

Marijuana Joint

Since the cannabinoids in marijuana look and act the same as the kind your body makes, they're able to slip by and latch onto the cannabinoid receptors in your brain. There are two types (that researchers know of): CB1, which are mostly located in areas of the brain that are associated with learning, memory, reward, anxiety, pain, and movement control, and CB2, which is associated with the immune system. The cannabinoids throw your usual system out of whack, boosting certain signals and interfering with others. Which is why marijuana's effects can range from a feeling of relaxation and pain relief to clumsiness, anxiety (or lack thereof), and even the munchies.

The Short-Term Effects

Just how quickly do you feel those results? Well, it all depends on whether you smoke, vape, or consume edibles.

“When you smoke, [cannabis] is in the bloodstream very quickly,” Rudroff says. “When you eat it, it can take up to 20 or 30 minutes before you can feel the effect.”

You've probably heard that sativa produces feelings of euphoria and enhances energy while indica is good for pain management and sleep (these experiences are echoed on just about every weed forum on the internet). Discriminating the effects of Cannabis sativa and Cannabis indica: a web survey of medical cannabis users. Pearce DD, Mitsouras K, Irizarry KJ. Journal of alternative and complementary medicine (New York, N.Y.), 2014, Sep.;20(10):1557-7708.

“The whole thing about strains is that we have no scientific basis that they will produce different experiences,” Carlini says. She and Rudroff both say this is due to the amount of crossbreeding that's happened—it’s tough to track the plants' botanical origins. (Remember how we mentioned earlier that scientists can’t agree on how many species exist?)

“For us as scientists, it’s all about the levels of THC and CBD,” Carlini says. “It’s very hard to say, ‘Purple Haze [a popular strain of weed] is sativa, and it has X effect.’”

That’s not to say that science can’t pin down any effects. For instance, if you’ve ever smoked pot and felt anxious—it’s likely you smoked something with a high level of THC.

“Doses that are THC dominant can provoke paranoia,” Carlini says, “but good luck on having an equation on when that is going to happen.”

In other words, weed experiences are highly individual. What produces paranoia in one subject might be an OK blaze for another. Likewise, while science can explain certain feelings like muscle relaxation and hunger, the exact formula needed to replicate an identical reaction in everyone—well, that’s a lot trickier.

“We don’t doubt the differences, it’s just not well understood from the perspective of science,” Carlini says. “It’s a very complex plant.”

In the Long Run

Weed Leaf
As for the consequences of habitual pot use, the jury is out. One recent study found that using pot regularly for 20 years resulted in higher incidences of gum disease but not much else. Another study that measured cognitive performance found that middle-age users had poorer verbal memory than their nonusing counterparts. And a different study found chronic users had “smaller hippocampus and amygdala volumes.” (Those are the sections of the brain that create new memories and control the “fight or flight” mechanism, respectively. Having "smaller volumes" means less capacity for those functions.) What’s more, long-term studies like these often depend on self-reporting techniques, which aren’t always the most reliable.

“We don’t know much about the long-term effects of cannabis,” Rudroff says. "In my opinion, cannabis does not lead to physical and mental dependence as long as it is used in a responsible manner." However, he does add that effects seem to be highly dependent on the age at which you start using. Those who start at a younger age—when the brain is not fully developed—tend to have more negative effects later in life.

The Bottom Line

Researchers have only scratched the surface of this powerful plant. It's getting a lot of buzz for everything from pain relief to its potential to treat certain cancers, but a lot still isn't known. Regardless, we think it’s fair to say this plant deserves some respect, whether you choose to partake or not.

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