New Opioid Painkiller Offers Strong Relief Without the Risk of Addiction

Medicine has a long-standing goal to find a drug as effective as morphine but without the risk of addiction. Scientists at the National Institutes of Health (NIH) may have finally found a new opioid painkiller that meets this need. This compound comes from a very unlikely source.

Researchers discovered DFNZ, which stems from a class of synthetic opioids called nitazenes. Scientists shelved these drugs in the 1950s because they were too dangerous for patients. Today, these analogues often appear in illegal drug supplies and cause fatal overdoses. These facts make the findings in the journal Nature particularly striking.

A Powerful Discovery From Discarded Chemistry

The story of DFNZ began with a different molecule called fluornitrazene (FNZ). NIH researchers studied FNZ to see if it could help with brain imaging. During this process, they found something much more important.

The body metabolises FNZ into DFNZ. Early tests showed that FNZ entered rat brains quickly and caused dangerous breathing problems. However, DFNZ behaved differently.

Dr Michael Michaelides from the National Institute on Drug Abuse (NIDA) led the study. He noted that DFNZ has a unique pharmacology. It provides strong pain relief but acts like a partial agonist in certain settings. This suggests the new opioid painkiller could be much safer for human use.

Why This Non-Addictive Opioid Analgesic Works Differently

Most opioid candidates fail because they are not strong enough. DFNZ is different because it is a superagonist. It activates the mu-opioid receptor with incredible efficiency. Usually, high efficiency means a high risk of overdose. Drugs like fentanyl flood the brain and stop breathing. DFNZ avoids this trap.

Two proteins at the blood-brain barrier pump DFNZ back out before it can build up. This limited penetrance keeps the drug from reaching dangerous levels in the brain. When scientists blocked these pumps, DFNZ caused the same breathing issues as fentanyl. This proves the barrier is the key to its safety.

This non-addictive opioid analgesic does not suppress breathing at therapeutic doses. In fact, brain oxygen levels actually increased during tests. Rats also did not develop a tolerance after a month of daily use. When researchers stopped the drug, the animals showed almost no withdrawal symptoms. Morphine caused eight distinct symptoms, while DFNZ caused only one.

Breaking the Cycle of Reward and Craving

Addiction happens when drugs cause rapid spikes in dopamine. These spikes reinforce the habit of drug-seeking. DFNZ does not trigger these spikes. Instead, it promotes a slow and steady increase in background dopamine.

The researchers believe a specific receptor complex in the brain reward hub limits the drug’s impact. This ensures the new opioid painkiller provides relief without creating a powerful “high.”

In lever-pressing tests, rats did not crave DFNZ. If researchers replaced the drug with saline, the rats stopped pressing the lever immediately. Heroin users usually continue seeking the drug even when it is gone. DFNZ did not trigger relapse behaviour in these animal models.

A Potential Tool for Recovery and Treatment

This new opioid painkiller could also treat opioid use disorder. Analgesic doses of DFNZ helped rats reduce their heroin intake. It might function like methadone but without the risk of respiratory failure.

The opioid crisis remains a major threat. In 2023, overdoses killed over 80,000 people in the United States alone. A drug that treats pain safely would be a massive public health victory.

Moving Toward Human Trials With Caution

Human trials are still far away. All current data comes from rodent studies. Biology does not always translate perfectly from mice to humans. DFNZ also still carries a very small rewarding effect. It is not a “zero risk” drug.

Nora Volkow is the director of NIDA. she believes a highly effective pain medication without addiction risks would change medicine. This new opioid painkiller is a major step in that direction. The team now plans more studies to ensure patient safety.

Source: dbrecoveryresources