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Marijuana, meanwhile, produces a chemical called THC that attaches to the second class of receptors (discovered in 1988). These receptors were then deemed “cannabinoid receptors,” and the brain chemicals that attach to them were called endocannabinoids (for endogenous cannabinoids). Because molecules in these plants attach to these receptors in our brain and elsewhere, they can, in small amounts, enhance our lives. Marijuana can calm the nausea in chemotherapy patients and improve the appetite of AIDS patients. Morphine and other opioids, of course, numb pain and allow for surgery to take place. In the bowels, opioids can control diarrhea—as Paul Janssen knew when he invented loperamide. But in larger quantities, far beyond what the brain can produce, these molecules prod our brain receptors to excess. THC in marijuana overwhelms the cannabinoid receptors and produces ravenous hunger and faulty memory. The morphine molecule locks with the opioid receptors to produce euphoria and numb pain. Opioid receptors in our lungs govern breathing; too much morphine molecule shuts down breathing, which is how overdose victims die. The morphine molecule also produces constipation in addicts. In withdrawals, without the drug, addicts suffer diarrhea. (Naloxone, the overdose antidote, is occasionally used to treat constipation.) (Interestingly, the natural substances that make humans high actually evolved in their plants as pesticides, to keep predator insects from feasting on their leaves. Nicotine is a pesticide that tobacco naturally produces. So is caffeine in coffee, cocaine in the coca leaf, morphine in the opium poppy, and perhaps THC in marijuana as well.) In
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Sam Quinones (The Least of Us: True Tales of America and Hope in the Time of Fentanyl and Meth)