To understand why opioids exert such a powerful pull on human beings, you want to look first to our brains’ natural “happy juice”: endorphins.
So says Charles Chavkin, a professor in the University of Washington’s Pharmacology Department.
Chavkin explains that there is a whole series of neural receptors designed specifically to detect endorphins.
“They’re there as kind of antennas,” he says. “They’re very specific. They’re tuned to one frequency. The one frequency is the chemical they’re evolved to detect. So they’re there pretty much waiting for the right time to fire.”
But opioid drugs mimic those endorphin molecules, and fool those neurons into firing. And because the drugs stay in our system much, much longer than a natural burst of endorphins, opioids overwhelm our neural pleasure networks. That can create a lower pain sensitivity, and a sense of euphoria, which is a dream-like state experienced physiologically, Chavkin says.
But as the brain gets used to that abnormally spiked level of chemicals, it turns down down its natural signaling in response, and tolerance starts to build up. Chavkin says that physical dependency can create a teeter-totter like affect.
“When the drug comes on one side of the teeter-totter and pushes it down, the physiology restores the balance. Now when the morphine is gone: Bam! The teeter totter tips the other way,” says Chavkin.
People who continue to use opioids tend to lose interest in the things that used to make them happy. The things they enjoyed previously are no longer enough to excite the desensitized pleasure networks, creating a dependence on the opioid in order to feel happiness and pleasure.
“There’s no doubt that there’s an element of choice, at least at the beginning. No one’s holding a gun to your head to do that. You will be taking the drug of your own choice. But what we know in the biology is that at some point, after an experiencing of that opioid for an extended period of time, individuals can’t quit,” says Chavkin