Although most organizations rely on urine tests for drug screening, some use hair testing, especially law enforcement agencies. According to Greek medical school professor Vassiliki A. Boumba and colleagues in their article for "International Journal of Toxicology," laboratories can compensate for hair thickness and other features that may cause differences.
The average hair sample includes about 120 strands. If hair is unavailable from the head, it can be used from other parts of the body, although the tester needs to know the source. Hair on the head grows about a half an inch per month, so if the sample size is an inch and a half, drugs are detectable for up to 90 days of past use.
Cocaine
German toxicologist F. Musshoff and colleagues in their article for "Forensic Science International," note cocaine can be detected in urine for only up to three days after it is consumed. In contrast, hair testing can detect cocaine in cases where urine screens were negative because if the sample size is at least an inch and a half, cocaine will show up it if has been used in the past three months. As a result, if long-term cocaine use is being investigated, hair testing is a good choice.
Hair testing for cocaine and other drugs can be used to exonerate or implicate individuals in some cases. For example, according to Mark L. Miller, Ph.D., research chemist for the FBI Academy and colleagues in their monograph for the National Institute of Drug Administration, a child died from cocaine intoxication, and the husband and wife each said the other was a frequent cocaine user. Hair testing exonerated the mother and proved the father was a chronic cocaine abuser.
Phencyclidine
Hair samples can be tested for phencyclidine--PCP--one of the drugs that is routinely tested for by the federal government in both urine and hair tests. Assuming that the hair sample is at least an inch and a half, use of PCP in the last 90 days will be detectable.
Marijuana
When hair testing for marijuana is performed, the tester is seeking the concentration of tetrahydrocannabinol--THC--and thus the presence of marijuana or hashish will be detected. Since urine tests can detect marijuana use for at least 30 days after ingestion, some organizations prefer urine testing to hair testing when marijuana is the suspected drug. On the other hand, hair is impervious to tampering and some individuals use various means to try to "beat" the urine test.
Amphetamines
The amphetamine screen for hair includes amphetamine, methamphetamine, MDMA and MDA. Thomas Mieczkowski, Ph.D. noted in "Mayo Clinic Proceedings" that hair or fingernail analysis is better than urine screening if amphetamines are suspected because amphetamines quickly clear the urine while evidence of amphetamine abuse remains in hair and nails for an extended period. As noted, if the sample size is at least an inch and a half, then the hair will reveal evidence of amphetamine for up to 90 days.
Opiates
Hair can be tested for opiate use, including such drugs as morphine and codeine. More specialized testing can detect for other opiates such as heroin and hydrocodone, according to Boumbas.
References
- Omega Laboratories: Hair Testing FAQ
- "Analysis of Saliva, Hair and Sweat for Drug Testing"; in Pharmacology and Abuse of Cocaine, Amphetamines, Ecstasy and Related Designer Drugs; Enno Freye; 2009
- "Journal of Chromatography A"; Hair Analysis for Illicit Drugs by Using Capillary Zone Electrophoresis-Electrospary Ionization-=Ion Trap Mass Spectrometry: Rossella Gottardo, et al. 2007
- "Mayo Clinic Proceedings"; Hair Analysis for Detection of Psychotropic Drug Use; Thomas Mieczkowski, Ph.D; April 2006
- "Forensic Science International"; Results of Hair Analyses for Drugs of Abuse and Comparison with Self-Reports and Urine Tests; F. Musshoff, et al.; 2005
