In fields, warehouses, squats, apartments or even in clubs, thousands of young people party every weekend by taking all kinds of synthetic drugs with euphoric effects. Every weekend, at least one is in for a bad trip. It's more or less serious, lasting or transitory, but it always turns into a nightmare.

The chemistry of some substances gives access to an entire section of the subconscious usually locked away. The bare elements of our personal lives, including the most painful ones, come out all mixed up and bad thoughts can become unbearable. A bad trip lasts as long as the product is efficient, generally, for five to six hours. Beyond that, if the high doesn't wear off completely, it can make the person addicted to the substance. The feeling of ecstasy provoked by visual hallucinations can degenerate at any time into an anxiety attack linked to the synthetic drug's effect on the central nervous system.

The "twilight sky in a delicate blue" described by Alfred Hofmann, the inventor of LSD, can transform into a crushing lead ceiling. The brain perceives innocent ants as giants, an imaginary row of gothic pillars transform themselves into a sight of devastated ruins that make you want to run away. Friends become dangerous rats, dogs are seen as octopuses and the panic crisis to escape from a giant fly can lead a person to jump out a window.

"The lethal effects linked to a hyperthermia crisis, when the body's temperature raises to 42°C, do exist, but they are very rare. We also see comas caused by overdoses or drug combinations," explains a neurobiologist specialized in that field. Extreme situations are no longer strictly associated to synthetic drugs. Last month, a teenager in France who took cannabis threw himself from a fourth floor. Both legs are now paralysed.