A false positive drug test is a screening result that reads positive for a drug class the person did not take. It happens because a rapid cassette reacts to a class of compounds, not one exact molecule, and some ordinary medicines are documented to cross-react. Other positives are real but have an ordinary explanation, such as a valid prescription. Below is what can cause a false positive drug test on each of the 14 panels Testr reads at every visit, and what laboratory confirmation does about it.
What a false positive is
Every Testr visit is the same 14-panel rapid urine screen, read on site by a certified collector. Each panel is an immunoassay strip. It reads negative below its screening cutoff and presumptive positive at or above it.
The antibody on each strip is built to react to a family of related compounds. A different compound can sometimes bind to the same strip and reach the cutoff. When that happens, the strip has reacted to a look-alike, and the result is a false positive. That is why an on-site positive is recorded as presumptive: it is a screen, not a measurement.
Two other situations are sometimes called false positives, but they are not errors by the strip. A valid prescription for the drug a panel screens for can read positive, because the drug is there. And a few ordinary exposures put the real compound in urine. Both are covered below, panel by panel.
The three validity strips, for pH, oxidants and creatinine, are a separate matter. They check the specimen, not a drug class, so they are not part of the list below.
What can cause a false positive, panel by panel
These come from the notes on each panel's own page. Each panel name links to that page, with its screening cutoff and detection window.
Amphetamine drug test (AMP): a valid ADHD prescription can cause a positive.
Barbiturates drug test (BAR): a valid prescription can cause a positive. Phenobarbital is still prescribed for seizures, and butalbital appears in some migraine medicines.
Buprenorphine drug test (BUP): an expected positive for anyone prescribed Suboxone.
Benzodiazepine drug test (BZO): a valid prescription for Xanax, Valium, Klonopin, Ativan or another benzodiazepine can cause a positive. Two unrelated medicines, sertraline (Zoloft) and oxaprozin (Daypro), are documented to cross-react on benzodiazepine screens. Those two are true false positives: neither is a benzodiazepine.
Cocaine drug test (COC): no common prescription contains cocaine. Two documented exposures produce a genuine positive, not a false one: cocaine is still used as a topical anesthetic in some ear, nose and throat procedures, and coca leaf tea contains enough to read positive.
EtG alcohol test (ETG): heavy exposure to alcohol-based products like hand sanitizer or mouthwash can occasionally cause low-level positives.
Fentanyl drug test (FEN): a valid fentanyl prescription can cause a positive.
MDMA and ecstasy drug test (MDMA): no cross-reactant is listed for this panel. Its note is about the pill, not the strip: pills sold as MDMA frequently contain other substances, so a broader screen matters more than the label on the pill.
Methamphetamine drug test (MET): certain prescriptions and some cold-medicine ingredients can trigger a screen.
Opiates drug test (MOR): codeine or morphine prescriptions, and even poppy seeds, can cause a positive.
Methadone drug test (MTD): an expected positive for anyone prescribed methadone.
Oxycodone drug test (OXY): a valid oxycodone prescription can cause a positive.
PCP drug test (PCP): no prescription contains PCP. It has no accepted medical use in the United States, so a valid prescription does not explain a positive. A few common medicines, among them dextromethorphan in cough remedies, venlafaxine and tramadol, are documented to cross-react on PCP screens.
THC and marijuana drug test (THC): some legal CBD products contain enough THC to cause a positive result. That is THC actually present, from a product sold as CBD.
The short codes are printed on the cassette and on the report. What each drug test abbreviation means lists them all, including the other spellings some cups use, such as MOP and FYL.
What happens after a presumptive positive
The collector records each panel exactly as read and does not interpret it. If you take a prescription, you can tell your collector at the visit. A valid prescription is accounted for at the laboratory stage, described below.
A rapid strip cannot tell a look-alike apart from the real drug. That takes a laboratory.
With the Rapid Test with Laboratory Confirmation, the sealed specimen goes under chain of custody to a CAP-accredited laboratory. The laboratory uses LC-MS/MS, which identifies the specific compound actually present and reports a measured level for it, in about 72 hours. Where a strip could only say "benzodiazepines," laboratory confirmation names the compound and its measured level. The menu covers 81 substances across 31 drug classes, and it lists several of the medicines named above in their own right, among them sertraline, dextromethorphan and tramadol.
Every laboratory report is reviewed by a Medical Review Officer (MRO), a physician who reviews laboratory-confirmed results and accounts for valid prescriptions before the report is released.
If you booked the At-Home Rapid Test, you can still add this step. Upgrade to laboratory confirmation in the app within 2 hours of collection, while the specimen is still viable. The post on deciding on laboratory confirmation within the 2-hour upgrade window walks through the timing, and how to read a Testr drug test result explains negative, presumptive positive and laboratory-confirmed.
Booking a test with laboratory confirmation
When a result will be acted on, the Rapid Test with Laboratory Confirmation is the one to order. Book in the Testr iOS app or book a drug test online. A certified collector can be at your door across the Los Angeles area in as little as 3 hours, in 30-minute arrival windows from 7 AM to 7 PM, seven days a week. The collector arrives in plain clothes and an unmarked vehicle and verifies identity with the 4-digit PIN shown in the booker's app. Every order carries a chain-of-custody code.
Results are released privately to the account holder in the app or at testrla.com/account, or to a named third party with the account holder's written consent. A therapist, psychologist or family-law professional can book for a client as a "someone else" booking, with the client's consent recorded at booking. There is more on drug testing for therapists and family-law professionals.
Testr performs non-DOT urine testing only.
Questions people ask
What can cause a false positive drug test?
Some medicines are documented to cross-react: sertraline and oxaprozin on the benzodiazepine panel, and dextromethorphan, venlafaxine and tramadol on the PCP panel. Valid prescriptions, poppy seeds and some legal CBD products can also cause positives.
Can Zoloft cause a false positive for benzodiazepines?
Sertraline (Zoloft) is documented to cross-react on benzodiazepine screens, as is oxaprozin (Daypro). Laboratory confirmation names the compound actually present and its measured level.
What causes a false positive for PCP?
Dextromethorphan in cough remedies, venlafaxine and tramadol are documented to cross-react on PCP screens. No prescription contains PCP, so a valid prescription does not explain a PCP positive.
Can CBD make you test positive for THC?
Some legal CBD products contain enough THC to cause a positive result. That is THC actually present, not a look-alike compound.
Can poppy seeds cause a positive drug test?
Yes. Poppy seeds, like codeine or morphine prescriptions, can cause a positive on the opiates panel.
What if I think my drug test result is a false positive?
You can mention any prescription to the collector during the visit. Laboratory confirmation by LC-MS/MS names the specific compound and its measured level in about 72 hours. An At-Home Rapid Test can be upgraded to it in the app within 2 hours of collection.