New Synthetic Opioid: ‘Iso’ Associated with Overdose Deaths

Published August 17th, 2020 by Dr. Miriam Opara, PharmD
Fact Checked by
Chris Riley

Isotonitazene, commonly called ‘Iso,’ is considered one of the most persistent and prevalent new opioids in the United States. It is a new synthetic (also known as human-made) opioid causing overdose deaths at an exponential rate. 

Iso is causing 40 to 50 overdose deaths a month in the United States, compared with an average of 6 overdose deaths per month in the summer of 2019. 

Opioid Epidemic Battle 

The ongoing battle of combatting opioid overdose deaths has been going on since the early 1990s. Overdose deaths first started with prescription opioids, then a rapid increase of overdose deaths involved heroin, and the third wave of overdose deaths involving synthetic opioids, like fentanyl, began in 2013. 

The CDC reports that in 2018, nearly 70% of the 67,000 deaths involved an opioid. 

Opioid overdose deaths have been increasing because of the availability of potent synthetic opioids on the black drug market. 

In April 2019, China announced a ban on the unauthorized production of fentanyl in response to the pressure from the United States federal government for China to provide more oversight on fentanyl production. Since then, new synthetic opioids, like Iso, have been on the rise. 

Iso is obtained through unregulated sources; therefore, the identity, purity, and dosage may result in significant adverse health risk. 

What is Iso?

Iso is a member of the benzimidazole family of opioids, which includes etonitazene, metonitazene, and clonitazene. This group of opioids is thought to have similar or higher potency to fentanyl. Iso was found to be 500 times more potent than morphine in an animal study. 

Iso is designed to mimic the effects of etonitazene. The DEA classifies etonitazene as a schedule I controlled (a.k.a. illegal) substance because it has high abuse potential. 

Iso can quickly enter the brain and cause effects on the central nervous system (CNS). The higher the dose consumed, the greater effect the drug will have on the body. The major side effect that leads to life-threatening overdoses is respiratory depression (slowing down of breathing). 

Since Iso is a new synthetic opioid, users have no experience taking the drug. This increases the risk of accidental overdose deaths because it is unknown what dose will cause certain effects. 

The risk is exceptionally high if users don’t know they are taking Iso, which may be the case when it is sold in the illegal opioid market.  

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Iso Hits the Streets

Iso can be found in both free base and salt form. It has been reported to be in brown, yellow, and white powders, as well as identified in liquid form. 

In March 2020, Iso was found in 1,900 fake pharmaceutical pills in Nova Scotia and Newfoundland. The drug was pressed into tablets to resemble Dilaudid (also known as hydromorphone). The Iso pill is a white triangular tablet with rounded corners that has an “M” on one side and the number “8” on the other side. The danger is that people may think they are taking a different drug. 

Iso was identified in at least 18 deaths in the United States between August 2019 and January 2020. The Center for Forensic Science Research and Education (CFSRE) reported that by the end of May 2020, Iso was identified in 180 cases

Death investigations associated with Iso, showed Iso was used in combination with one or more psychoactive substances, suggesting that multiple drugs were laced or used together. Many cases involved the use of benzodiazepines, which are also CNS depressants and lead to respiratory depression and potentially death. 

Detecting Iso 

Because Iso is a new drug, many law enforcement and healthcare personnel have not heard of the drug. Therefore, detecting Iso is a challenge because it does not show up on routine drug screening. Iso needs to be added to toxicology tests to understand the extent of the problem. 

If a patient shows up to the emergency department with signs of an opioid overdose, but the opiate testing is negative, the missed diagnosis could have deathly consequences. 

An important part of combating the opioid epidemic has been the distribution of the overdose reversal drug Narcan. Narcan can temporarily reverse an overdose while it is happening. Iso may respond to Narcan, but because it has a high potency, it may require several doses for it to be effective.

The State of Ohio Board of Pharmacy was the first to issue a proposal to place isotonitazene as a Schedule I opiate. The board found Iso to have a high potential for abuse, no accepted medical use, lack of accepted safety, and poses a risk to public health. 

In June 2020, the DEA issued a notice for a temporary order to schedule isotonitazene in schedule I of the Controlled Substances Act. This action will help to regulate the manufacturing and distribution of the drug in hopes of decreasing the rise of Iso.  


  • Centers for Disease Control and Prevention. Understanding the Epidemic. Published 2020. Accessed 31 July 2020.
  • State of Ohio Board of Pharmacy. Proposal To Permanently Schedule Isotonitazene. Published 2020. Accessed 31 July 2020.
  • Drug Enforcement Administration. Schedules of Controlled Substances: Temporary Placement of Isotonitazene in Schedule I. Published 2020. Accessed 31 July 2020.
  • Drug Enforcement Administration. Drugs of Abuse A DEA Resource Guide. Published 2017. Accessed 31 July 2020.
  • National Association of Drug Diversion Investigators. ‘Iso,’ a Deadly New Synthetic Opioid, Has Hit American Streets. Published 2020. Accessed 31 July 2020.
  • Los Angeles Times. China to regulate all fentanyl drugs, keeping promise to Trump. Published 2019. Accessed 31 July 2020.
  • Kuwabara Blanchard S. Why Isotonitezene Is Not Yet the “New Fentanyl”. Published 2020. Accessed 31 July 2020.
Published August 17th, 2020 by Dr. Miriam Opara, PharmD
Fact Checked by
Chris Riley

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