Spice - Among the most popular psychoactive substances available on the market are ones that replicate the doping effect of cannabis.
"Spice" is one of the brands which has gained notoriety following reports of its widespread use in prisons. It comes as a smoking mix and has been known to cause paranoia and hallucinations when taken.
The Prison Officers Association this month named spice and similar substitutes such as "black mamba" as contributing to a rise in deaths, serious illness and self-harm among inmates.
Laughing gas - Otherwise known as nitrous oxide or "nos" and dubbed "hippy crack" by the press, laughing gas comes in canisters and is used recreationally after being inhaled, often out of balloons.
It gives users a light-headed, euphoric feeling that lasts for several seconds, but, due to it depriving the body of oxygen, can be fatal when taken in excess.
A number of footballers have found themselves at the centre of scandals after being filmed taking the drug. The gas is conventionally used in catering to assist in the making of whipped cream.
Salvia - Unlike other synthetic legal highs, salvia comes from a plant. It is still sold in many so-called headshops, but only on the proviso that it is not marketed for human consumption.
When smoked or chewed, it can create a hallucinogenic experience. This carries the risk of triggering a psychotic episode in someone with existing or latent mental health issues.
Mephedrone - In 2010, mephedrone - which also goes by the name "mcat" and "meow meow" - shot into the public spotlight following a string of deaths.
It mimicked the effects of many amphetamines such as speed and MDMA, providing similar feelings of elation, but with a potentially deadly impact on the heart and central nervous system.
Within months it was outlawed and is currently a class B drug.
Benzofuran - More recently, the Government was forced to clamp down on the sale of benzofuran, which became known as benzo fury.
In its most widely recognised form, it was sold as tablets and purported to be a legal alternative to ecstasy, allowing it to establish a foothold in the underground rave scene.
Its side-effects include anxiety, aggression and in some cases psychosis. It became a class B drug in 2014 and has been linked with several deaths in the UK.
Annihilation - Another synthetic cannabinoid similar to Spice and Black Mamba - it is made to act like the active chemical in cannabis.
The drug has sparked an urgent police warning after several people collapsed in Rochdale after taking it. Symptoms include profuse sweating, a racing heartbeat and delirious ranting.
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