LEGAL highs are unregulated psychoactive compounds marketed as legal alternatives to well-known controlled drugs.

The term "legal high" is applied to a wide range of synthetic and plant-derived substances and products, including herbal highs, party pills, and research chemicals, many of which may be specifically designed to circumvent existing drug controls.

They are usually sold via the internet or in "smart shops" or "head shops". The chemicals they contain have, in most cases, never been used in drugs for human consumption. Users can not be certain what they are taking and what the effects might be. There have been a number of deaths linked to legal highs.

Some drugs marketed as legal highs contain ingredients that are illegal. Test purchasing in Scotland found that one-fifth contained controlled drugs.

Several of the legal high tablets tested contained aramethoxymethylamphetamine (PMMA), which is believed to have caused at least 19 deaths in Europe since summer 2010.

Some substances previously sold as legal highs are now controlled under the Misuse of Drugs Act, including mephedrone or meow meow, naphyrone and BZP. This means they are illegal to possess or to supply to others.

A recent report from the European Monitoring Centre for Drugs revealed that manufacturers are producing one new legal high a week.