Products such as the SafeCare combined test are designed to detect drugs in human urine. In rare cases, however, certain foods, drugs and other substances can cause false positive results.
Let's look at some of the most common causes of erroneous results.
Secondhand smoke from marijuana
If you find yourself in an environment where marijuana is smoked, your urine may contain traces of tetrahydrocannabinol (THC), even if you haven't smoked directly. THC is a natural ingredient and the main psychoactive substance in cannabis. The chances of having enough THC to trigger a positive drug test result are very slim, though.
Weight loss pills
Phentermine is a prescription drug that helps curb appetite. It is chemically similar to amphetamines, and is a stimulant used to treat attention deficit hyperkinetic disorder.
Poppy seeds
Poppy seeds naturally contain morphine and codeine. A poppy seed bagel, for example, could cause you to test positive for both opioids within a day of eating it. This is more likely to happen in laboratories that still follow the older, lower detection thresholds for these substances.
Products containing ethanol
Many liquid medications, vanilla extract and breath fresheners often contain ethanol, the main active ingredient in alcoholic beverages. Today's drug tests can detect traces of alcohol long after consumption. If you use a product or medicine that contains ethyl alcohol, your urine sample may give a false positive result.
Antidepressants
Sertraline is prescribed for depression, panic attacks, obsessive-compulsive disorder, etc. Some drug tests may not be specific enough to distinguish sertraline from benzodiazepines. The latter is an older sedative drug often found in people who overdose on opioids. A false test result can occur several days after you stop taking an antidepressant.
Antibiotics
Drug tests usually do not respond to antibiotics, but some are known to produce false positives. Rifampin, which treats tuberculosis, can be detected as an opiate in some rapid urine tests. Moreover, a false positive result may be possible even more than 18 hours after you have taken the antibiotic.
Antihistamines
Some popular over-the-counter allergy and sleep medications contain diphenhydramine, which is a type of antihistamine. Drug tests may misread this drug as methadone, which helps people get off heroin or other opiates and can lead to addiction. Diphenhydramine can also be mistaken for the illegal hallucinogen PCP.
Coca tea
This drink is a popular folk medicine in Peru and other South American countries. It is made from the leaves of the same plant that cocaine comes from. Coca tea can give a false positive result up to 36 hours after use.
Antipsychotic drugs
Several psychiatric medications can lead to false positive drug test results. Quetiapine, which treats schizophrenia and bipolar disorder, can falsely show that you have methadone in your urine. Another antipsychotic -- chlorpromazine -- can result in positive drug tests for amphetamine.