New York, Feb 3: Smoking synthetic marijuana sold under names such as "K2" and "Spice", may not be a safe substitute to natural marijuana, but may lead to dangerous side-effects, including seizures, psychosis, dependence and death, researchers have warned.

The synthetic cannabinoids (SCBs) are man-made mind-altering chemicals that are either sprayed on dried, shredded plant material so they can be smoked (herbal incense) or sold as liquids to be vaporised and inhaled in e-cigarettes and other devices (liquid incense) and thus cause adverse health effects.

"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," said Paul L. Prather, a pharmacologist at the University of Arkansas.

The primary psychoactive compound in marijuana, delta-9-tetrahydrocannabinol (THC), activates two receptors CB1 -- found in high abundance in the brain and central nervous system -- and CB2, found primarily in the immune system.

In the study, published in the journal Trends in Pharmacological Sciences, the team found that although they activate the CB1 and CB2 receptors, the SCB compounds and other cannabinoids are otherwise chemically distinct from marijuana and often from each other.

As a result, they may be activating other cellular receptors in addition to CB1 and that these receptors could be responsible for some of the adverse health effects seen in the users.

The SCB compounds are more potent than delta-9-THC, as "these are highly efficacious drugs. They tend to activate the CB1 receptor to a greater degree than we can ever get to with THC from marijuana," added William E. Fantegrossi, a behavioural pharmacologist at the University of Arkansas.

Another risk is that these are often sold as safe alternatives to marijuana that, because of their chemical structures, will not be discovered through standard drug screenings.

Thus, users who purchase these drugs over the internet or elsewhere simply do not know what they are getting.

"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," Fantegrossi said.

Why smoking synthetic weed may not be safe