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.

​This table is NOT all inclusive for potential positives and/or negatives. Refer to specific commercial product details for more information about the sensitivity of the specific commercial assay.

​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