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A vaccine to protect against fentanyl’s deadly effects is headed for clinical trials in humans.
The vaccine, which showed positive results in studies of mice and rats, is designed to block fentanyl from entering the brain, blocking its effects and preventing overdoses.
If approved, it would become the first treatment to prevent overdoses of fentanyl, which is the leading cause of drug overdose death, statistics show. This is different than treatments like naloxone, which reverse the effects after an overdose.
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How it works
The vaccine is designed to create antibodies against fentanyl, which keeps the drug from crossing the blood–brain barrier. It contains a synthetic fragment of fentanyl attached to a protein called CRM197, along with dmLT, an immune-activating compound.
Around $4 million worth of fentanyl seized by the LAPD. The experimental vaccine is designed to create antibodies against fentanyl, keeping the drug from crossing the blood–brain barrier. (LAPD)
This combination stimulates the immune system to produce antibodies that capture fentanyl in the bloodstream before it can reach the brain, according to the University of Houston’s Colin Haile, co-founder and scientific adviser of ARMR Sciences, which licensed the vaccine.
“In a vaccinated individual, those anti-fentanyl antibodies are in the blood,” Haile told Fox News Digital. “So if they consume fentanyl, the antibodies grab onto the drug and prevent it from getting into the brain. They would feel no effects if they ingest fentanyl — absolutely none. And they would not overdose.”
Eventually, he said, the fentanyl would be eliminated from the body.
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In the mice and rat studies, the animals still had antibodies against fentanyl six months after vaccination, added Haile, who is also a research associate professor of psychology at UH and a founding member of the UH Drug Discovery Institute.
While some have questioned whether such a vaccine would indirectly encourage drug use, Haile pointed out that for vaccinated people, the drug would have “no euphoric effects,” so those seeking a “high” would not get it.
Fentanyl has been known to be mixed with other substances, such as marijuana. (iStock)
The main benefit, according to Haile, is that the vaccine would reduce the potential health dangers of fentanyl.
“Respiratory depression is the primary effect that induces death from this highly potent synthetic opioid,” he said.
Headed for trials
Following successful testing in mice and rats, the first human clinical trial is slated to begin in early 2026 at the Center for Human Drug Research, which is associated with the University of Leiden in the Netherlands.
“They would feel no effects if they ingest fentanyl — absolutely none. And they would not overdose.”
The small phase 1 trial will enroll about 40 participants, focusing on safety and immune response.
After the phase 1 trial for safety, a phase 2 trial will test whether the vaccine effectively blocks fentanyl’s effects in humans.
Potential risks and limitations
The primary limitation is that data is so far only available for mouse models, and it’s unknown how effective the vaccine would be in humans.
Haile told Fox News Digital that there were no adverse side effects reported in the animal study, likely because the ingredients of the vaccine are proteins that have already been used in other combinations in humans, so their safety profile is already known.
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“Also, unlike other vaccines, we use extremely low doses of the components,” he noted. “We have put the vaccine into a lot of animals and have not seen any adverse side effects at all.”
Even in a toxicology study, during which the researchers administered 20 times the dose of the vaccine that would be given to humans, they still saw no overt signs of toxicity, according to Haile.
Potential use cases
Haile mentioned several different use cases for the vaccine, primarily those with opioid use disorder who want to quit using fentanyl. It could also be used by first responders and healthcare workers who want to reduce the risk of accidental exposure.
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Military and national security personnel could also benefit from the vaccine, Haile said, as it could help protect against fentanyl and fentanyl-like compounds that have been used as chemical threats.
Finally, parents may be seeking protection for at-risk teens or young adults, as fentanyl has been known to be mixed with other substances, such as marijuana.
Dr. Marc Siegel, senior medical analyst for Fox News, said the progress of the vaccine is a “very exciting advance with a huge upside.” (iStock)
Looking ahead, Haile said this could pave the way for the approval of other anti-drug vaccines, such as cocaine and methamphetamine, which are already in the works.
“If we can tackle the primary ones — fentanyl, cocaine and methamphetamine — we will be saving hundreds of thousands of lives,” he added.
“This is likely to prevent many overdoses where a patient is sedated and stops breathing as a result of fentanyl.”
Dr. Marc Siegel, senior medical analyst for Fox News, said the progress of the vaccine is a “very exciting advance with a huge upside.”
“I am very glad it is now entering human trials — it is being very well-studied,” he told Fox News Digital. “This is likely to prevent many overdoses where a patient is sedated and stops breathing as a result of fentanyl.”
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The antidote for fentanyl (Narcan) is limited because fentanyl lasts for many hours, but the Narcan (an opioid antagonist) wears off after only a few hours and has to be readministered, Siegel pointed out.
“You want to make sure this vaccine is limited to those really at risk for opioid overdoses and addiction, because fentanyl is also a useful pain medication for cancer and a useful agent for anesthesia,” the doctor added.
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The vaccine was developed with funding from the U.S. Department of Defense and licensed to biotech startup ARMR Sciences.