Researchers have developed a vaccine that blocks the high produced by the drug fentanyl in mice, according to Popular Science.

Last year the Drug Enforcement Administration issued a nationwide alert in response to a surge in overdose deaths from heroin laced with the narcotic drug fentanyl, the most potent opioid available for medical use.

In the new study, the Scripps Research Institute scientists injected mice with fentanyl molecules three times over the course of six weeks. After that, it was impossible to get the mice high, regardless of how much fentanyl the mice were given.

The vaccine contains a molecule that mimics fentanyl’s core structure. When a mouse received the vaccine, its immune system produced antibodies to neutralize it. The antibodies bind to the drug and keep it from reaching the brain. The researchers say that in theory, blocking the ability to feel a high could stop drug-seeking and drug-taking behavior.

The researchers took some of the mice’s blood and combined it with fentanyl molecules, and found the antibodies killed the drug molecules. They observed that vaccinated mice given fentanyl did not demonstrate “high” behavior (such as ignoring discomfort). In addition, antibodies generated by the vaccine protected the mice against overdose.

The fentanyl vaccine would not eliminate the high produced by other opioids such as heroin or oxycodone, the article notes. The researchers hope to study a mixed vaccine for fentanyl and heroin.

“The importance of this new vaccine is that it can block the toxic effects of this drug, a first in the field,” lead researcher Kim Janda said in a news release.

The study is published in the journal Angewandte Chemie.