Cross-reactants are molecules which are very similar to the substance being tested for. When someone has consumed these recently, there is the chance that it will show as a false positive result.
Discovering these tends to be a case of trial and error – it can be hard to predict beforehand whether any given substance will cause issues.
There aren’t many cross-reactants, compared to the infinitude of medications and substances available to consume!
Here’s a list of medications that can give false positive readings for amphetamines. Most of these are fairly rare, and some of these have been withdrawn and are no longer available legally.
- Buflomedil, used for treating artery disease. Brand name Loftyl.
- Brompheniramine, an antihistamine. Brand name Dimetapp.
- Chlorpromazine, used to treat psychosis, severe depression, and nausea. Brand names Thorazine and Largactil.
- Fenfluramine, an amphetamine derivative used to treat seizures. Brand name Fintepla.
- Isometheptene, used to treat migraines. Brand names Amidrine and Nodolor.
- Mexiletine, used to treat abnormal heart rhythms and chronic pain. Brand names Mexitil and NaMuscla.
- A metabolite of procainamide, which is used for the treatment of cardiac arrhythmias. Brand name is Procainamide.
- Perazine, used to treat psychosis. Generic drug.
- Phenmetrazine, used to suppress appetite and also as a stimulant. Withdrawn from the market, as it was widely abused. As an example, in 1963 Lee Harvey Oswald was in custody for the assassination of JFK. A nightclub owner named Jack Ruby walked to the police headquarters and shot Lee Harvey Oswald, who died within a few hours. Jack Ruby was on phenmetrazine at the time!
- Phentermine, a weight loss medication which is also a form of amphetamine. Brand name Ionamin.
- Phenylpropanolamine, a decongestant. Brand names Proin, Propalin, Cystolamine, Uricon and Uriflex-PT.
- Promethazine, an antihistamine. Brand name Allersoothe.
- Quinacrine, anti-malarial and also used to treat some skin conditions. Brand names Mepacrine and Atabrine.
- Ranitidine, used for treating reflux. Brand names Zantac, Ranitidine and Peptisoothe.
- Tolmetin, an anti-inflammatory drug. Brand name Tolectin.
There is nothing certain about any of the above. When in doubt, ask for advice and send the sample to a laboratory for confirmation testing.
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