Nitrous oxide is a gas that can make people feel relaxed, euphoric and giggly, leading to its nickname "laughing gas".
It is not illegal to be in possession of the substance, sometimes also known as "hippie crack", although it is prohibited from being sold in England and Wales to under-18s if there is a risk they will inhale it.
According to the government-funded drugs helpline FRANK, there is a risk of unconsciousness or even death from lack of oxygen - the nitrous oxide effectively pushes the oxygen out of the body.
The risk is increased if the gas is taken in an enclosed space or if a plastic bag is used that covers both nose and mouth.
"Mixing nitrous oxide with alcohol is especially dangerous," the helpline says.
It can cause dizziness and heavy regular use can lead to severe vitamin B12 deficiency, which can cause serious nerve damage. Regular use also inhibits the formation of white blood cells and the immune system.
While the gas can be legitimately used for pain relief in dental procedures, in engines to make them perform better, and in aerosol cans to prevent food going off, there have been concerns at its use as a so-called legal high.
A Home Office campaign last year on the risks of legal highs showed that laughing gas was the second most popular drug among young adults in 2013/14 after cannabis, being more widely used than powdered cocaine and ecstasy.
Research by the Local Government Association also described as "deeply disturbing" the notion that many young people view nitrous oxide as safe, despite it being linked to a number of deaths.
Seventeen-year-old Joseph Benett suffered a cardiac arrest after taking the popular party drug in 2012. The promising art student fell into a coma but later died.
In September last year three revellers became ill at a nightclub in Bolton after suffering a suspected bad reaction to laughing gas.
Police were called to Royal Bolton Hospital amid reports the patients were suffering from the effects of drug ingestion.
It was thought they may have inhaled nitrous oxide, but they were said at the time to be recovering well.
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