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Turns out it's kind of hard to come up with a good prop for a show about illegal psychoactive compounds that aren't going to get you in pretty significant trouble, so I got nothin'. [SciShow Intro] But today, we are talking about Delta-9-Tetrahydrocannibanol, otherwise known as the major biologically active substance in the Cannabis plant, otherwise known as marijuana. So here it is: The molecule, not the marijuana. No matter what you think of this compound or how familiar you may be with it, there is no denying that THC...pretty potent. Its effect stems from its ability to bind to receptors in your brain called cannabinoid receptors and the reaction that takes place after that binding occurs. Now, calling them cannabinoid receptors is kind of misleading. It makes it sound like they're designed to be stimulated by cannabis. They're not. They're receptors located on neurons and they're activated by chemicals called neurotransmitters, which basically allow neurons to communicate with each other. Cannabinoid receptors are found in all different parts of the brain. Their highest density occurs in the areas of the brain responsible for pleasure, thinking, memory, coordination, time perception. Normally, these cannabinoid receptors are not activated by cannabis, they're activated by a chemical called anandamide. And that neurotransmitter plays a large role in making short-term connections between nerve cells. It's also largely responsible for the brain's ability to forget things, which is very useful in our normal, daily lives. We can't remember everything. And it seems to have a hand in regulating our eating behavior as well as generating sensations of pleasure. Its name, anandamide, which is kind of a beautiful word, comes from the Sanskrit word for "inner bliss." Anandamide, for what it's worth, has been found in chocolate. Anandamide and THC belong to the same class of chemicals, which we call cannabinoids. By mimicking anandaninde, binding to and activating those receptors, THC interferes with normal functioning of your brain. Well, your brain is now on drugs. By attaching itself to a neuron, THC screws up communication between other neurons. Let's say Neuron 1 needs to tell Neuron 2 to do something, like remember a phone number or hit a baseball with a baseball bat. Well, if THC is bound to one of those neurons, that communication is more likely to fail, and the person is less likely to remember that thing or hit that baseball. So, roughly, that's how THC affects the brain. But there are some other obvious interesting questions here, like: Why on earth would a plant decide to make a chemical that does this? What--why? To paraphrase the author Michael Pollan, a plant does not go through the expense of making such a complicated and extraordinary molecule--and continuing to produce it--if it isn't doing that plant some good. It turns out no one knows for sure why marijuana produces THC, but there are some fascinating theories. The first: THC turns out to be really good at absorbing UV radiation, and so it's possible that, since marijuana often grows at higher elevation, that it needs the ability to absorb that radiation without, you know, harming the plant. THC also has some antibiotic properties, so it's possible that that's how it's helping out plants. It also may help us out. Scientists have done studies and found that THC is a fairly potent antibacterial. And third is my absolutely favorite reason, and that's, um, that other animals have these cannibanoid receptors, too. And it's possible that, uh, leaf-eating insects have them, and that THC is there to put them on drugs so that they, like, forget where they found that delicious plant. And they're like, "Ah, man, I had that really good plant yesterday, but I can't remember where I found it." And then they just end up, like, eating Cheetos outside of a 7 Eleven at 2 a.m., which, you know, if you're a beetle...that's not so bad. I live in Missoula, Montana. It's a college town, fairly high pot smoking population here. Also a very high deer population, and I'm starting to wonder... The deer are always walking around downtown with this, like, glazed look over their eyes, and I'm thinking maybe they're getting into somebody's stash. And now they're all addled, can't find where they found that delicious brick of marijuana on someone's back porch. They're just walking around downtown, hoping, hoping beyond hope that they'll stumble across one again. Animals on drugs. It's no laughing matter. If you want to know more about the science of THC, our citations are, of course, always down in the description. If you want to ask us questions, uh, or suggest topics for us here on SciShow, you can connect with us on Facebook or Twitter or down in the YouTube comments below. [Credits]