A vaccine that could be used to treat heroin addicts could be on the way, after successful trials in primates. The vaccine, which has been developed at the Scripps Research Institute (TSRI), blocks the "high" of heroin, and has been shown to be effective up to eight months after being administered.

This is the first vaccine against an opioid to pass this stage of testing, and the researchers hope that they will now be approved to move on to clinical testing.

It works by teaching the immune system to produce antibodies against heroin, and the psychoactive products within it that cause the high users experience. The vaccine does this by exposing the immune system to part of the heroin molecule's structure.

Then when heroin is next introduced into the system, the newly created antibodies will target it, neutralizing the heroin molecules. Users (in this trial, rhesus monkeys) don't feel the euphoria from heroin, because the heroin molecules are blocked before they can reach the brain.

“This validates our previous rodent data and positions our vaccine in a favorable light for anticipated clinical evaluation,” study leader Kim Janda said in a statement. “We believe this vaccine candidate will prove safe for human trials."

The hope for the vaccine is that it can be used to treat heroin addicts, by removing the high they get from the drug, and their motivation for taking the drug at all. This could help prevent relapses in addicts recovering from addiction.

The trial saw rhesus monkeys being injected with the vaccine, before being given doses of heroin. The researchers found that four of the monkeys that were given three doses of the vaccine had an effective immune response, which could neutralize various doses of heroin. The vaccine was found to be most effective in the first month after vaccination, but the effect could last for over eight months.

Two of the four monkeys tested had been pre-vaccinated with the same vaccine in a previous study, seven months prior to this one. Raising hopes of an effective long-term vaccine for heroin, these two monkeys showed a much higher response to the vaccine in this second round of experiments. If this effect is replicated in humans, this could mean that heroin addicts could be given long-term immunity to heroin, helping with their recovery.

This research, which was published in the Journal of the American Chemical Society, looked at heroin only, and wouldn't be effective against other opioids. However the same logic can be applied, and a previous study by TSRI showed that a vaccine for "designer drug" Fentanyl was effective in mice.

The next step for the team will be to license the vaccine to an outside company for partnering in clinical trials.