A group of Mexican researchers is working on a vaccine that could reduce addiction to one of the world’s most notorious narcotics: heroin.

If all goes as planned in an upcoming human trial of a potential heroin vaccine, a new weapon may soon be available to combat heroin addiction in drug users.

Researchers at the country’s National Institute of Psychiatry say they have successfully tested the vaccine on mice and are preparing to test it on humans to see if it exhibits the same beneficial effects.

The vaccine, which has been patented both in Mexico and in the United States, works by making the body resistant to the effects of heroin, so users would no longer get a rush of pleasure when they smoke or inject it, rendering the narcotic effectively useless.

“It would be a vaccine for people who are serious addicts, who have not had success with other treatments and decide to use this application to get away from drugs,” the institute’s director Maria Elena Medina said in Mexico City on Thursday.

Maria Elena Medina, director of the National Institute of Psychiatry, speaks about the patent of a new vaccine that could reduce addiction to heroin, during a news conference at the institute in Mexico City

The Scripps Research Institute in California, which has also seen success of its heroin vaccine in lab rats, is currently conducting human clinical trials for cocaine and nicotine vaccines, but not heroin.

The Mexican researchers will be the first to test a heroin vaccine in humans. The scientists are hopeful a breakthrough is on the horizon, as their vaccine appears promising.

Health Secretary Salomon Chertorivski earlier projected that the vaccine will not be ready for human use for five years. However, that estimate may be a conservative one now that country is set to begin human trials.

Scientists worldwide have been searching for drug addiction vaccines for several years, but none have yet been fully developed and released on the market. One group at the US National Institute on Drug Abuse has reported significant progress in a vaccine for cocaine.

However, the Mexican scientists appear to be close to making a breakthrough on a heroin vaccine.

During the tests, mice were given access to deposits of heroin over an extended period of time. Those given the vaccine showed a huge drop in heroin consumption, giving the institute hope that it could also work on people, Maria Elena Medina said.

Mexico, a major producer and transit country for drugs smuggled into the US, has a growing drug addiction problem and grapples with relentless drug-related violence. Health Secretary Jose Cordoba recently said the country has some 450,000 hard drug addicts.