Banned legal high Spice could cause seizures, psychosis and addiction and could even kill, warns new research.
The synthetic marijuana was considered a 'safe' alternative to cannabis.
But scientists have now linked it to a range of dangerous and potentially deadly side effects.
Sold under names such as Spice and K2, synthetic cannabinoid compounds (SCB's) activate the same receptors as marijuana but are chemically distinct meaning they can't be discovered through drugs screenings.
SCB's and the primary psychoactive compound in marijuana activate two receptors - the CB1 found in the brain and central nervous system and the CB2 found primarily in the immune system.
The chemicals were made illegal in May last year after they were linked to more than 100 deaths in the UK and a rise in violent assaults in prisons, but they continue to be popular with teens across the country.
Scientists from the University of Arkansas in the US noted a catalogue of acute and long term adverse effects in SCB users, including seizures and convulsions, kidney injury, cardiotoxicity, strokes, anxiety, and psychosis in susceptible individuals.
They also reported people becoming tolerant to the chemicals, suffering from withdrawal and becoming dependent on them - as well 20 deaths linked to SCB use.
Because SCB's are chemically distinct from marijuana, there's a chance they may be activating cellular receptors other than CB1 which could be responsible for some of the adverse side effects.
SCB's are also more potent than marijuana, and activate the CB1 receptors to a greater degree - achieving a more intense high.
Study leader Dr Paul Prather said: "It started in the early 2000s in Europe, and in the U.S, in 2007 or so, we started seeing all kinds of people coming into emergency rooms saying they smoked marijuana, but then they had these really bizarre symptoms that did not correspond with the effects you see with marijuana.
"The public sees anything with the marijuana label as potentially safe, but these synthetic compounds are not marijuana, ... you never know what they are, and they are not safe."
Despite being made illegal in Britain Spice and K2 are still widely available online, meaning users don't know exactly what they are getting in each purchase and further increase the risk to their health.
Behavioural pharmacologist Dr William Fantegrossi who also worked on the study said: "Not only does the amount of the active pharmacological agent change with different batches of drugs, made by different labs, but the active compound itself can change."
"And there are usually a minimum of three, if not five, different synthetic cannabinoids in a single product," added Prather.
The authors still believe that the therapeutic use of cannabinoids, to help relieve symptoms in neurological conditions and some cancers, can still provide significant benefits but warn against improper use.