A testing kit that lets parents detect whether a child is using drugs using a lock of hair is now available in Britain.

The £40 kit is claimed to reveal seven drugs including cannabis, cocaine, Ecstasy and heroin. Confirm Biosciences, the American manufacturer, says it can detect molecules that remain in the hair for up to 90 days, “equipping parents with a valuable new tool for combating substance abuse”.

The company says the test is more sensitive and reliable over a much longer period than saliva or urine tests. Shampoo, bleach or other external chemicals did not affect the results.

Users of the tests, available online, send off a sample for testing and then receive a report on the amount of each drug detected as well as the frequency of use.

Figures released this week show that more than 11,000 under-16s were treated for addiction to cannabis, heroin and alcohol in 2007-08.

But Martin Barnes, chief executive of the charity Drugscope, said that he opposed drug testing within the family “which could create barriers, destroy trust and ultimately do more harm than good”.

“Many parents are understandably anxious about drugs, but it is important to be informed, remain calm and keep communication open if they suspect a child is using them,” he said. “Parents need to build up a degree of trust with their child, so that a son or daughter feels they can talk honestly about their drug use and how to get help with it.

“This kind of relationship could be at best, damaged, and at worst, destroyed, if a child fears they are going to be drug tested by their own family.”

The Department of Health said that drug use among young people was declining but that increasing numbers of teenagers were entering treatment.

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