Amphetamine can be detected in urine for two to three days after ingestion. The half-life of amphetamine is between seven and 32 hours, depending on urinary pH. The half-life increases with higher urinary pH due to free amphetamine reabsorption by the kidney tubules. Lower pH decreases the half-life. The half-life can also increase with repeated use and accumulation of the drug.
Interpretation of positive amphetamine results can be quite challenging due to its similarity in structure to many over the counter drugs, as well as prescription drugs. Diet formulations and decongestants such as ephedrine, pseudoephedrine, phentermine, and phenylpropanolamine are examples. Amphetamine is prescribed legitimately as Adderal.