7362951-powderThe active ingredient in the synthetic drug known as bath salts could be more addictive than methamphetamine, a new study suggests.

Scientists from the Scripps Research Institute allowed rats to self-administer either the bath salts compound MDPV or meth, by pressing a lever that delivered the substances intravenously, Forbes reports.

The scientists increased the number of lever presses needed for the rat to receive additional infusions of the drugs, to see how hard the rodents would work for it.

Rats pressed the lever about 60 times on average to receive a dose of meth, but pressed up to about 600 times for MDPV. "Some rats would even emit 3,000 lever presses for a single hit of MDPV," study author Shawn M. Aarde said in a news release. "If you consider these lever presses a measure of how much a rat will work to get a drug infusion, then these rats worked more than 10 times harder to get MDPV."

Rats addicted to MDPV displayed repetitive behavior, such as repeatedly licking the walls of their chamber. Humans addicted to bath salts also display repetitive behaviors, such as tooth grinding or compulsive skin-picking, Aarde noted.

The study appears in the journal Neuropharmacology.

Bath salts cause increased physical activity, sleeplessness, a lack of desire for food or water, and strong cravings to take more of the drug. Higher doses of the drug can lead to paranoia, violence and suicide.