Depending on the type of test and biologic matrices being tested, toxicology tests may have false positives or false negatives.
- False negative: undetected substance despite exposure. This may occur of the concentrations are below the limits of detection, beyond the time of detection, or the assay does not detect the substance despite being in the drug category.
- False positive: detected substance despite no exposure. This may occur if a drug has a similar structure to the drug category, such as dextromethorphan and PCP.
DRUG CLASSIFICATION |
POTENTIAL POSITIVES |
POTENTIAL NEGATIVES |
Amphetamines |
ADHD Medications Decongestants MDMA Buproprion Ephredrine Phenyethylamines |
|
Benzodiazepines |
Diazepam Temazepam |
Alprazolam Clonazepam Lorazepam Midazolam |
Cannabinoids (Marijuana) |
Promethazine Efavirenz |
Synthetic cannabinoids Cannabidiol (CBD) |
Opiates |
Codeine Heroin Morphine |
Semi-synthetic opioids (oxycodone, hydrocodone, etc) Synthetic opioids (fentanyl, methadone, etc) |
Phencyclidine (PCP) |
Dextromethorphan Ketamine Diphenhydramine Venlafaxine |