Getting a new job or adopting a child are two reasons why you may be required to have a drug test. These tests typically examine a sample of urine for the presence of alcohol, marijuana, amphetamines, benzodiazepines, barbiturates, phencyclidine (PCP), cocaine, lysergic acid diethylamide (LSD) or strong painkillers called opioids. But urine drug tests are not perfect and many prescribed and over-the-counter drugs can yield a false-positive test. This is especially likely if the drugs or their breakdown products have a chemical structure that is similar to the tested drugs. Drugs that may cause false-positive urine drug tests include certain antibiotics, cold medicines, psychiatric medications and painkillers.
Antibiotics, Cold Medicines and Antihistamines
One of the most common antibiotics, amoxicillin (Amoxil), can cause a false-positive test for cocaine. Quinolones, a group of antibiotics including ofloxacin (Floxin), levofloxacin (Levaquin) and ciprofloxacin (Cipro), may produce false-positive tests for amphetamines and opioids. Rifampin (Rifadin), an antibiotic frequently used to treat tuberculosis, can also lead to a false-positive result for opioids. A false-positive LSD test may occur in people taking the antibiotic cephradine (Velosef).
Ephedrine and pseudoephedrine, ingredients often found in decongestants or cold medicines, can cause a false-positive test for amphetamines. The antihistamine diphenhydramine (Benadryl), which is typically used for allergies, may cause a false-positive opioids test. Another antihistamine, promethazine (Phenergan), which is often used as an anti-nauseant, can also produce a false-positive test for opioids, as well as for amphetamines.
Diazepam (Valium), a common anti-anxiety drug, can cause a false-positive result for alcohol. Another anti-anxiety medication, buspirone (Buspar), can produce a false-positive LSD test. Many antidepressant medications can cause false-positive tests for LSD, including bupropion (Wellbutrin), fluoxetine (Prozac), desipramine (Norpramin), imipramine (Tofranil), amitriptyline (Elavil), trazodone (Desyrel), sertraline (Zoloft) and doxepin (Sinequan). Sertraline can also produce a false-positive test for benzodiazepines, while bupropion and trazodone can give a false-positive test for amphetamines. A false-positive PCP test can occur in people taking venlafaxine (Effexor), another antidepressant, and lamotrigine (Lamictal), a medication for bipolar disorder and seizures.
Chlorpromazine (Thorazine), a medication used for schizophrenia and other conditions with psychotic symptoms, can produce false-positive tests for amphetamines, opioids and LSD. Other antipsychotics, such as thioridazine (Mellaril), haloperidol (Haldol) and prochlorperazine (Compazine), can also cause a false-positive LSD test. People taking quetiapine (Seroquel), an antipsychotic medication for schizophrenia, depression and bipolar disorder, can have a false-positive test for opioids.
Use of nonsteroidal anti-inflammatory drugs (NSAIDS), such as ibuprofen (Advil, Motrin) or naproxen (Aleve), may lead to false-positive tests for marijuana, barbiturates and PCP. Certain opioid painkillers, such as tramadol (Ultram) and meperidine (Demerol), can produce a false-positive test for PCP. Another opioid painkiller, fentanyl, can produce a false-positive test for LSD. Midrin, a combination anti-migraine medication containing acetaminophen and two other drugs, may give a false-positive reading for amphetamines.
Proton pump inhibitors, such as pantoprazole (Protonix), are a group of drugs used to treat ulcers and acid reflux. They can give a false-positive test for marijuana. Ranitidine (Zantac), an acid-reducing drug also used for these conditions, can yield a false-positive result for amphetamines. A false-positive LSD test can occur in people taking metoclopramide (Reglan), a drug used for esophagus disorders or as an anti-nauseant.
Labetalol (Normadyne), a medication to lower blood pressure, can give false-positive readings for amphetamines and LSD. Verapamil (Isoptin) -- used for high blood pressure and heart problems -- can cause a false-positive test for opioids, while its close relative, diltiazem (Cardizem), can produce a false-positive LSD test. People taking methylphenidate (Ritalin, Concerta), which is typically used for attention deficit and hyperactivity disorder, may have a false-positive test for LSD. A common diabetes medication, metformin (Glucophage), can lead to a false-positive result for amphetamines.
Whether taking a drug will actually cause you to have a false-positive urine drug test will depend on various factors, including the amount of the drug you are taking, when you took the last dose and the exact type of urine drug test used. Furthermore, there are other drugs in addition to those mentioned above that will sometimes cause a false-positive test. So if you are taking any prescription or over-the-counter drugs, it would be wise to bring them to the drug test so they can be recorded by the tester.
Because urine tests are not perfect, they are usually considered to be just screening tests. If your test is positive, your urine sample will generally be sent to a specialized lab for retesting with a more accurate test to determine whether the result is real or a false-positive.
Reviewed and revised by: Mary D. Daley, M.D.