Researchers at University College London have tested a nasal spray containing a natural painkiller on animals, finding that it alleviated pain in the animals without them showing signs of becoming tolerant to its effects. Without a build-up in tolerance, users may be less likely to risk an overdose.

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Ijeoma Uchegbu, who is leading the research, explained to The Guardian that “if people don’t develop tolerance, you don’t have them always having to up the dose. And if they don’t have to up the dose, they won’t get closer and closer to overdose.”

Uchegbu explained that scientists have long seen the potential for natural opioids, specifically because the body does not build up a tolerance to them in the same way as synthetic opioids like fentanyl and oxycodone. However, securing their journey to the brain is more complicated, as they are broken down in the liver when injected into the bloodstream.

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The spray the researchers are testing sends the natural opioid directly into the brain via millions of soluble nanoparticles, which they hope will help overcome this hurdle. They are now raising funds to run a human clinical trial to determine the spray’s safety. The volunteers will receive the nasal spray and then be tested to see whether it helps them endure the pain of putting an arm in ice-cold water. If this trial is successful, the spray will be tested for its pain relief abilities on patients with bone cancer who suffer severe and sudden pain.

With opioids claiming the lives of nearly 100 people a day in the U.S., the researchers hope that natural opioids will offer an alternative and help combat the crisis.