Modafinil and/or its major metabolite, modafinil acid, may be quantified in plasma, serum, or urine to monitor dosage in those receiving the drug therapeutically, to confirm a diagnosis of poisoning in hospitalized patients, or to assist in the forensic investigation of a vehicular traffic violation. Instrumental techniques involving gas or liquid chromatography are usually employed for these purposes. In 2011, modafinil was not tested for by common drug screens (except for anti-doping screens) and is unlikely to cause false positives for other chemically unrelated drugs such as substituted amphetamines.
Reagent testing can screen for the presence of modafinil in samples.