New fentanyl vaccine is entering human trials — here’s how it works
A vaccine that blocks the effects of fentanyl — including overdose — will enter human trials in the coming months, perhaps paving the way for the first-ever proactive treatment for opioid use disorder.
The first trials will focus on evaluating the safety of the vaccine, initially developed with funding from the U.S. Department of Defense. The vaccine has already been tested on rats and has shown promising results. It has now been licensed by startup ARMR Sciences, which will begin recruiting patients for phase I clinical trials in the Netherlands in 2026, starting in January or February.
How does the vaccine work?
The vaccine works by keeping fentanyl out of the brain, which it does by making the molecule a target of the immune system.
Fentanyl is a synthetic opioid with effects 50 times more potent than heroin. Opioids, also called narcotics, work largely by binding to opioid receptors in the brain and spinal cord, triggering changes in nerve cell signaling that prevent pain and can create a euphoric effect.
But these opioid receptors are also found in the part of the brain that controls breathing, so fentanyl can also reduce breathing to a lethal degree if used in excess. A dose of 2 milligrams of fentanyl – a volume similar to about a dozen grains of salt – can be fatal, according to the Drug Enforcement Agency (DEA).
If a person overdoses on fentanyl is treated with naloxone (better known by the brand name Narcan), relatively quickly these effects can be reversed. This antidote also binds to opioid receptors, blocking the effects of fentanyl.
The ARMR vaccine takes a different approach: it works in the circulatory system, before the drug reaches the brain.
“This would be the very first treatment that does not work on the [opioid] receiver,” Gage told Live Science.
What is in the vaccine?
To prevent fentanyl from reaching the brain, the immune system must first recognize the drug. But fentanyl is a tiny molecule, not a pathogen like a virus, and immune cells don’t naturally respond to its presence.
To stimulate an immune response to fentanyl, the University of Houston Colin Haileco-founder and scientific advisor of the ARMR, and his colleagues must have associated the opioid with something else.
They chose a deactivated diphtheria toxin called CRM197, a compound already used in vaccines on the market; once deactivated, the toxin is no longer toxic and helps elicit an immune response. To further boost this immune response, they also added dmLT, a compound distilled from toxins produced by the immune system. Escherichia coli bacterium. This modified compound is not toxic in itself and has also been tested in humans in trials of other not yet approved vaccines.
These two components are attached to a synthetic piece of the fentanyl molecule, which by itself cannot cause euphoria or pain relief.
When the immune system encounters this combination of fentanyl fragments, CRM197 and dmLT, it builds antibody that react to real fentanyl. These antibodies bind to the opioid, preventing it from passing through the brain’s protective membrane – the blood-brain barrier – and then eliminating it from the body.
In rat studiesThe vaccine prevented fentanyl from entering the rodents’ brains and also prevented the drug from depressing breathing and causing an overdose.
How is the vaccine tested?
Studies of the vaccine so far have focused on rodents, although dmLT and CRM197 respectively have been tested to some extent and are already used in other vaccines in humans. The protocol in rats involves giving an initial dose of the fentanyl vaccine, then boosters three and six weeks after the first dose, Haile told Live Science.
“The longest we followed the animals in our studies is about six months, and we saw a complete blockade of the effects of fentanyl six months after the initial vaccination,” Haile said. It remains to be seen how that translates into “human years,” he noted, but lab rats live a few years in total, so researchers believe the vaccine will work for a long time in humans.
The first human trials which will begin in early 2026 will recruit 40 people and focus on detecting any safety issues with the vaccines, such as unwanted or dangerous side effects. Researchers will also take blood samples from participants to ensure the vaccine stimulates the creation of anti-fentanyl antibodies.
If these phase I trials are successful, the next step will be phase II trials to test the vaccine’s effectiveness, that is, how well the vaccine blocks the effects of fentanyl. In these trials, not only will antibody levels be tracked over time, but some participants will also receive safe levels of fentanyl used to relieve pain during medical procedures. This will be done under close monitoring, to check that the vaccine works in the presence of the medicine.
Are there any potential harms to the vaccine?
Fentanyl has legitimate medical uses as a pain reliever, particularly in emergency situations. One concern about the vaccine is that people who take it will lose this option for pain relief.
However, the antibodies created by vaccination do not bind to other opioids — like morphine, oxycodone or methadone — or other options for pain relief, Haile said. This means there are alternatives if vaccinated people need long-term pain relief.
The drug also does not interfere with buprenorphinea medication used to treat opioid use disorder by reducing withdrawal symptoms and cravings. Haile said he and his team are currently testing the vaccine in combination with naltrexonea non-opioid medication also used to block the effects of opioids in the treatment of drug addiction.
In theory, it might be possible to take enough fentanyl to neutralize the body’s stores of anti-fentanyl antibodies, Haile said. However, because the vaccine blocks the euphoric effects of fentanyl, he expects that people who want to quit smoking will not be motivated to try to get around this problem.
“We want people who want to quit smoking to not want to do drugs,” he said. “This will give them a chance to realize that they won’t get high on this drug and that there’s no point in taking it any longer.”
Who could benefit from the fentanyl vaccine?
Gage suggested one market for the vaccine could be first responders concerned about accidental exposure to fentanyl. (That concern has increased in recent years with the spread of disinformation about fentanyl.)
For clarity: If fentanyl comes into contact with your skin through casual exposure (for example, if you touch an object that has been exposed to the drug), it will not be absorbed through the skin. Significant absorption through the skin requires direct contact on the medicine for hours or days. That said, if a paramedic or police officer puts the drug in their hands and then touches their mouth or eyes, they might feel some of the pain-relieving or analgesic effects of the drug, Haile said.
The vaccine could also be “another tool in the toolset” for people with opioid use disorder, Gage said. Combine the vaccine with “robust” cognitive behavioral therapya type of talk therapy and community support could be “incredibly beneficial for people who are just looking for another lifeline to help themselves get better,” he said.
Finally, the vaccine could benefit people who use less lethal drugs – such as cocaine, stimulants or painkillers – that they buy on the black market. This is because these drugs are increasingly cut with fentanylmeaning people can overdose without even knowing they are taking this opioid.
“I had two close childhood friends who died of fentanyl overdoses,” Gage said. “None of them were looking for him.”
More than 48,000 people died of opioid overdoses in 2024 in the United States, according to preliminary data. Perhaps because of the high number of deaths, early research suggests that people with personal experience of opioid use disorder and the general public perceive a potential fentanyl vaccine positively. Time will tell how the new vaccine performs in human trials, but if it’s ultimately approved, it could be the first tool of its kind against overdose deaths.
This article is for informational purposes only and is not intended to offer medical advice.
