On May 22, 2012, after working the evening shift at a coal mine in Galatia, Ill., Michael Jeter, then 34, took the sleep drug zolpidem (Ambien) even though he had to drive to a doctor’s appointment early the next morning. At some point he also took diphenhydramine, an antihistamine found in over-the-counter allergy drugs such as Benadryl and sleep aids such as Sominex, as well as an anti-­anxiety drug that can cause drowsiness.

Around 9:30 the next morning, after his doctor’s appointment, Jeter drove into a group of highway workers, killing one and injuring three. “The widow sent my son a family picture,” says Jeter’s father, the Rev. Michael Jeter. “Michael put it on the refrigerator to remind him what he had done.”

Brian Moore, 43, who was hit by Jeter and still recoverring from his injuries, is sympathetic. “I believe he didn’t realize that combining those pills was like putting a chemical bomb in his stomach.”

Jeter was arrested for aggravated DUI and sentenced to nine years in prison. But if you’re driving erratically because you’ve taken medication, you can get arrested even if you don’t harm anyone, says Duane Kokesch of the National District Attorneys Association.

If, after checking for dilated pupils, poor coordination, and other signs, a police officer suspects you’re impaired because of a drug you’ve taken, he can charge you with DUI and arrange for a blood test.

Editor's Note: This article also appeared in the February 2016 issue of Consumer Reports magazine.

These materials were made possible by a grant from the state Attorney General Consumer and Prescriber Education Grant Program, which is funded by a multistate settlement of consumer fraud claims regarding the marketing of the prescription drug Neurontin (gabapentin).