However, use of urine as the test meduim imposes practical limitations on the frequency of collection when these techniques are applied. Opiates and cocaine are water-soluble and quite rapidly excreted, generally within 48 to 72 hours. Use of Hair Testing Use of hair as a test medium avoids the limitations of infrequent urine testing. Hair testing is relatively well established and uses a number of the same technologies as urine-based tests, including enzyme, radioisotope, and fluorescent immunoassays. Urinalysis of a single specimen generally can detect the presence of drugs for a period of several days to a week or two, depending on the drug.
Hair analysis can detect drug use for several months or more, depending on the length of the hair.
Preliminary research shows that even treating hair with a variety of strong compounds will not completely eliminate traces of illicit drugs. Compared with urine samples, it presents fewer risks of disease trasmission. Some practical difficulties may occur in collecting specimens from individuals with short or no head hair. Metabolites are the biochemical products of the breakdow of drugs within the body. For cocaine, both urine testing and hair testing detect the drug metabolites rather than the illegal drug itself.