The use of opioid painkillers can result in constipation, so the last drug you might expect to see an opioid addict consume is the over-the-counter anti-diarrhea medication Imodium. What you might not know is that loperamide, the active ingredient in Imodium and its store-brand knock-offs, is itself an opioid — one that must be taken in very high, potentially lethal, doses to achieve any noticeable effects, but one to which a growing number of addicts are turning.

Loperamide has a very difficult time passing through the blood-brain barrier and having the typical opioid effect on the central nervous system, unless taken in significant amounts.

“If you take enough, it rushes the gate, and some penetrates the blood-brain barrier,” Dr. Chuck O’Connell, an emergency medicine physician and toxicologist at the University of California, San Diego, tells the NY Times. “Once it crosses the barrier, it can act on the central nervous system and you get euphoric effects.”

But at what cost? Ingesting large amounts of an anti-diarrhea medicine won’t just lead to troubling constipation; it could kill you.

The Annals of Emergency Medicine recently looked at the cases of two fatalities involving loperamide abuse.

In the first case, a 24-year-old man was trying to use loperamide to self-manage his opioid withdrawal. When his body was discovered, authorities found six empty boxes of loperamide at the scene.

“Autopsy findings revealed pulmonary and cerebral edema, urinary retention, moderate cardiomegaly, and lower extremity venous thrombi,” reads the report, which notes that the loperamide concentration in his blood was nearly 25 times the maximum level for therapeutic use of the drug.

The second case involves a 39-year-old man who had been using buprenorphine therapy to treat his opioid addiction, but then switched to using anti-diarrheal medication instead. He died suddenly after gasping for breath and collapsing. Lab tests on his blood turned up more than 45 times the maximum therapeutic concentration for loperamide.

The report urges doctors who see certain symptoms in emergency cases to ask patients about possible loperamide abuse, and to report cases of loperamide toxicity to the Food and Drug Administration’s MedWatch database.

The authors of that paper call for regulation limiting sales of loperamide — similar to the restrictions on sale of pseudoephedrine and dextromethorphan — in an effort to rein in unchecked abuse of the drug.

A rep for the FDA tells the Times that the agency “is aware of recent reports of adverse events related to the intentional misuse and/or abuse of the anti-diarrhea product loperamide to treat symptoms of opioid withdrawal or produce euphoric effects,” and that the FDA will review these reports and “take appropriate steps as soon as possible.”

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