Which is to say: Loperamide is extremely safe at recommended doses for treating diarrhea and extremely inefficient if the goal is getting a fix. Eggleston said he’s heard of people taking 400 or 500 tablets a day. “They put it in a blender and make a smoothie and drink it over one or two hours,” he said. It causes constipation but no worse than other opioids, which people who are addicted often manage by taking stool softeners or laxatives.

Loperamide is also available as a generic, and it is cheap. You can buy 400 tablets for little more than $10 online.

Unlike opioids prescribed as painkillers, loperamide doesn’t usually reach brain cells. A naturally-occurring protein called P-glycoprotein pumps the drug out of the brain. But at very high doses, loperamide overwhelms those pumps and floods the brain’s opioid receptors. Eggleston said that’s led some people to try taking a second over-the-counter drug that disables the pumps, so they can use smaller doses of loperamide. The long-term consequences of that combination are unclear, but once in the brain, loperamide has similar effects as other opioids: drowsiness, depressed breathing, and maybe even death in the worst cases.

But massive doses of loperamide also have a second surprising and deadly consequence. The drug blocks calcium channels, which affect the beating of the heart. Too much loperamide and the heart is unable to keep a regular rhythm. Somwail Rasla, an internal medicine resident at Memorial Hospital of Rhode Island, saw a 28-year-old man come in with a particular and unusual pattern in his EKG. “There’s no reason such a young patient should have it, except as a congenital abnormality or medication induced,” said Rasla. It was the latter. The man said he been taking 100 to 150 tablets of loperamide a day. He was put into the ICU and given magnesium to stabilize his heart rhythm. He survived. After nine days in the hospital, he was discharged.

“We felt like this case really needed to be published to increase the public awareness,” said Rasla. Until just a few years ago, the cardiac effects of loperamide were unknown even to most doctors—simply because people weren’t taking the drug in big enough doses until the opioid epidemic. And the trend is unlikely to go away soon. “We will see more cases because the more restrictions [there are] on opioids, the more doctors are afraid of trying to extend their prescriptions, the more people will seek different substances,” said Rasla.

The same thing happened with heroin, Eggleston pointed out. When doctors put the squeeze on prescription painkillers, people went looking for alternatives—many of them to illegal alternatives like heroin and fentanyl and some to legal ones like loperamide.

One proposed policy fix is making loperamide harder to buy, like requiring an ID the way stores now do with cough syrup containing dextromethorphan. That would put the squeeze on another end of the opioid supply though; it only works if the restrictions drive people to treatment rather than to heroin. Diarrhea-drug misuse is just a small, almost absurd part of the larger opioid epidemic.