Working at an opioid treatment center, I get questions frequently from patients who are concerned about their positive urine drug tests. Overall, the tests are pretty good, but false positives can, and do, occur. Every different lab tests the urine samples with different reagents, or chemicals, so the doctor at your opioid treatment center should know what can cause a false positive at your particular lab.
First, a little about cocaine. The test for cocaine is very specific. The only thing that causes a positive for cocaine is cocaine. Despite similarities in the name, Novocain and lidocaine don’t cause a drug test to be positive for cocaine. No, it can’t be absorbed through the skin enough to give a positive, and if you are so close to cocaine that you’re handling it, I would say that counts as a positive anyway. Yes, it can be absorbed through mucosal lining – oral, vaginal, rectal – and again, that’s a true positive.
Benzodiazepines are a different story. I’ve worked at clinics where diphenhydramine (Benadryl) causes false positive results. That is, the patient didn’t take benzos, but the diphenhydramine made their test positive, so it looked like they are using benzos.
I tell patients to avoid diphenhydramine, which can be difficult, since it’s in most of the over the counter sleep aids. But diphenhydramine does interact with the metabolism of methadone, and needs to be avoided.
I had a patient test positive repeatedly for benzos, and she swore she wasn’t taking them. I believed her, and had her gather all the medications she had at home, prescription and over the counter. When we looked at them, she had a bottle of some kind of herbal stress-relief medication. On a hunch I asked her to stop this pill. Within two weeks her urine drug screen was negative.
I’m convinced this herbal remedy either contained a benzo, or a substance that caused a positive for benzos. There’s no FDA oversight with these herbal remedies, so the contents may or may not actually be what’s listed on the label.
So if you are testing positive for benzos, and know you haven’t taken any, consider stopping any herbal medicines that you are taking.