Unlike hair, the most commonly used detection methods (blood and urine), cannot register long term use, nor can they always distinguish among different drugs, say the authors. Bleaching or straightening the hair will not erase the chemical evidence it holds.
Crystal meth boosts alertness and promotes a sense of wellbeing, euphoria, and exhilaration. It also curbs appetite and enhances sexual arousal. But long term abuse damages nerves in the brain and can lead to psychotic behaviour and aggression.
The drug is very easy to manufacture in home laboratories, and global use has soared, particularly among young women, say the authors. An estimated half a million Americans alone are thought to use it every week, including 5% of pregnant women.
The authors carried out hair sample analysis on more than 8,000 people, totalling more than 34,000 test results between 1997 and 2005.
In all, 396 samples tested positive for crystal meth, accounting for 8% of the total during this period. This number included 11 mother and baby pairs.
All but 14 of the samples testing positive for crystal meth had been sent for analysis in 2005. The first positive cases dated from 2003.
Wide ranging levels of the drug were found in both the mothers' and the newborns' hair samples. But the levels matched, indicating that the drug is able to cross the placenta directly to the developing fetus, say the authors.
Only one newborn had no evidence of the drug in its hair. Fetal hair starts to grow at about 20 weeks.
The authors say that the precise effects of crystal meth on a fetus are not fully known, but the evidence to date points to restricted fetal growth and developmental problems.
Source:BMJ Specialty Journals