Hair analysis for cannabinoids and amphetamines in a psychosis incidence study.

It remains often uncertain whether the use of illicit substances has contributed to the aetiology of psychosis. Gas chromatography-mass spectrometry can be used to detect them in hair of the head. Given a monthly growth rate between 1.0 and 1.5 cm, one can examine hair segments that originated during the pre-psychotic period. We examined the usefulness of hair analysis to detect the use of cannabinoids or amphetamines during this period. One hundred patients participated in a psychosis incidence study and 64 yielded hair. Refusal was associated with non-Dutch ethnicity, not with a clinical diagnosis of use. A monthly growth rate of 1.5 cm was assumed and 33 specimens were found to be long enough. Cannabinoids or amphetamines were detected in nine specimens. In seven they were not detected, whereas the patients had reported their use. It is likely that their hair grew at a slower rate and that the examined segments belonged to an earlier period of time, during which the substances were not used. Lack of knowledge about the individual hair growth rate is an important limitation to the usefulness of this method.