Published: 07/14/2026 | Author: Eric Owens

New research helps explain two things people in recovery from opioid use disorder have reported for years. Quitting fentanyl feels different, and relapse and overdose risk after time away from the drug is far more dangerous than people expect. 

A UCLA-led study finds that people who use illicit fentanyl daily in Los Angeles can build a tolerance to amounts that’s lethal for someone without that tolerance. That tolerance isn’t permanent, but explains why relapse after a period of abstinence is so often fatal. It also shows why folks who use fentanyl daily often have trouble starting medication for opioid use disorders, or MAT.

The Research Findings

The study was led by Drug Checking Los Angeles, a community-based public health program. It’s one of many centers out in The Golden State, which offers an impressive range of programs from inpatient care to local Narcotics Anonymous chapters.

Researchers analyzed the purity of more than 500 fentanyl samples tested between September 2023 and January 2026, then surveyed 47 people who reported using fentanyl daily or near-daily about their consumption patterns. The findings describe this specific group of frequent users, not fentanyl users as a whole.

Using morphine milligram equivalents (MME), a standard unit that lets researchers compare opioids of different strengths, the team calculated that this group of daily users consumed an average of about 8,887 MME per day. For context, the CDC considers 2 milligrams of fentanyl potentially lethal for someone with no opioid tolerance. Daily users in the study consumed roughly 60x that amount each day. Due to the tolerance built up through sustained daily use, they didn’t overdose at that level. That tolerance, built gradually, is the entire reason they could survive doses that would kill someone without it.

Raising Overdose Risk After Relapse

This is the main point for anyone in or near recovery: tolerance built through daily fentanyl use isn’t lethal for the person who built it, but it’s also not permanent. Tolerance begins dropping within days of stopping, whether that break comes from detox, incarceration, hospitalization, or completing a treatment program. If someone relapses and returns to the amount they used before stopping, that same amount can now be fatal because their body lost the tolerance that once made it survivable. 

This is one of the best-documented and most dangerous patterns in opioid overdose deaths. The study’s data on just how extreme fentanyl tolerance can become shows why the drop after even a short break risks your life.

Complicating Treatment

The same tolerance pattern has direct implications for anyone trying to start MAT. Buprenorphine is an effective medications for treating opioid addiction but can trigger precipitated withdrawal, a sudden and severe withdrawal reaction, if it’s started too early or at too low a dose for someone with this level of built-up tolerance. Clinicians have increasingly moved toward faster, higher-dose buprenorphine induction protocols specifically because standard low-dose approaches didn’t account for tolerance levels like the ones documented in daily users in this study.

Chelsea Shover, the study’s senior author and an associate professor at UCLA, relayed even a less pure fentanyl supply in other regions would still produce dramatic tolerance levels among daily users. “It’s no longer ‘how do we treat someone who smokes a gram of fentanyl per day,’ it’s ‘how do we treat someone using thousands of MMEs of oral morphine in fentanyl per day,'” Shover noted.

Harm Reduction After Any Break From Use

Anyone who has stopped using fentanyl, for any reason and for any length of time, faces heightened overdose risk if they return to it. Naloxone can save a life by displacing opioids from receptors in the brain. But for someone whose tolerance has dropped, even a single dose is no longer strong enough. Using a smaller amount of drugs than before, avoiding using alone, and having naloxone on hand are basic protections during this specific window of risk.

Methadone remains available as an alternative for people who need a different approach than buprenorphine, particularly those for whom induction has been difficult. Both medications work, and neither is a lesser path than the other.

NA Meetings & Peer Support During Recovery

Starting treatment after daily fentanyl use and staying in recovery afterward is rarely accomplished alone. NA meetings can provide steady peer support both during a demanding induction period and in the vulnerable weeks after any break from use, when relapse overdose risk is highest. Meeting with others who understand this specific risk can make the difference between a slip and a fatal overdose.

If you or someone you love uses fentanyl daily, or is returning to use after any period of abstinence, seek out others who understand what you’re going through before the problem escalates. Remember that NA meetings are free and confidential, and the fellowship there offers peer support during withdrawal, induction, and the early weeks after any break from use.

Simply call 800-934-1582(Sponsored) to get started or browse our directory for chapters located anywhere in the USA.