Janssen riffed off the piperidine ring over the next two decades, finding new molecules to hit the opioid receptors no matter where they were in the body. One place they reside is our bowels, which is why opiates create constipation. (Thus diarrhea is a common symptom of opiate withdrawal, as the body rebalances without the drug.) Janssen surmised that the piperidine ring might also be the basis for an antidiarrheal medicine. Trial and error led him to discover loperamide (brand name: Imodium), an opiate that attaches to receptors in our bowels but cannot cross the blood barrier into the brain
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