An epilepsy drug being tested for use in treating addiction can help obese rats shed weight, US government researchers said.
Their findings point not only to an easy treatment for obesity, but show it is similar to drug addiction, they said.
Even rats bred to be obese lost up to 19 percent of their weight and normal rats lost 12 to 20 percent of their weight after 40 days of injections of the drug, called vigabatrin or GVG, the team at the US Department of Energy's Brookhaven National Laboratory found.
"When we gave GVG, they would steadily lose weight, and when we took them off GVG, they would steadily gain weight," Amy DeMarco, who worked on the study, said in a telephone interview.
"It was like a roller coaster. It was also dose-dependent. Rats given higher doses would lose more weight." She added that her team saw no side effects in the rats.
Vigabatrin, sold as Sabril in Canada, Mexico and Britain by Sanofi Aventis, is being tested in people now for cocaine and methamphetamine addiction.
Writing in the journal Synapse, the researchers said the drug stops the brain's dopamine reward system, which underlies addiction and overeating.
"For substance abusers, the number one cause of relapse is environmental cues, triggers," said Brookhaven's Dr Stephen Dewey, who led the research.
"A fairly significant proportion of subjects who are obese suffer from something called binge eating disorders. They binge-eat based on cues. They see a cake, they smell a hamburger and they crave and they start to eat. One of the great things about this drug is it stops this," Dr Dewey added.
"Most drugs of abuse do the same thing to the brain. They increase dopamine. GVG can prevent that increase of dopamine," Ms DeMarco said.
Brookhaven has licensed its vigabatrin patents to Coral Gables, Florida-based Catalyst Pharmaceutical Partners Inc, which is testing the drug in phase II human trials for cocaine and methamphetamine addiction.
The company also plans to test the drug, which it calls CPP-109, for binge eating disorder and alcohol dependence.
Deerfield, Illinois-based Ovation Pharmaceuticals Inc is also testing the drug for use in cocaine and methamphetamine dependence.
Dr Dewey said he has been working with vigabatrin for decades. "It was impossible to get any pharmaceutical company interested in pursuing it for an addiction application," he said.
Britain's Royal College of Ophthalmologists reported in March that the drug can affect sight, reducing peripheral vision and limiting the field of vision in other ways, perhaps irreversibly.
Dr Dewey said these effects were seen with much heavier use of the drug than might be indicated for weight loss.