The National Advisory Committee on Drugs (NACD) is seeking to commission an overview of substances sold in headshops to increase its knowledge on legal drugs sold across the country.

The review will establish what the products are supposed to contain on the basis of their labelling and the actual chemical content of the substances.

It will also survey various headshops, including online shops, to determine how easy it is to gain access to what it describes as psychoactive substances.

A list of all the stores across the country will be compiled, and researchers will examine where the materials are sourced from.

According to the NACD, "user experience and published data will include psychological effects on cognition, mood and mental functioning as well as public health risks".

The researchers will also speak to A&E units about their experiences in dealing with people who have consumed products from head-shops.

Furthermore, the review will look at other countries' codes of conduct, to determine what measures are taken in other jurisdictions to restrict access to the substances.

A comparison will be drawn up to ascertain how best to tackle the increasing problem presented by the rising number of shops selling legal highs.

"Because the drugs they appear to contain have never been tested for safety in humans, we have to rely, at present, on user reports," said Des Corrigan, chair of the NCAD

"These may not be reliable because people often don't know what exactly they have taken and there is no way of knowing how much has been used.

"Nor do we know what other drugs might have been taken by users which could change the effects and risks."

Meanwhile, regulations which will outlaw a range of products sold as 'legal highs' are to be introduced before June, the Department of Health has indicated.

In 2006, the department introduced regulations which banned psychotropic mushrooms, otherwise known as magic mushrooms. Last year it banned BZP, which was at the time a legal alternative to ecstasy.