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What Is the Most Potent Opioid?
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What Is the Most Potent Opioid?

Written by
Kara Rogers
Kara Rogers is the senior editor of biomedical sciences at Encyclopædia Britannica, where she oversees a range of content from medicine and genetics to microorganisms. She joined Britannica in 2006 and...
Kara Rogers
Fact-checked by
Britannica Editors
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
Britannica Editors
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The most potent opioid is generally considered to be carfentanil, which is used in veterinary medicine, primarily to tranquilize elephants and other large mammals. Although some formulations of the illicit opioid nitazene can reach or exceed the potency of carfentanil, many others are less potent. The most potent opioid approved for medical use in humans is sufentanil.

Carfentanil and sufentanil are synthetic opioid drugs that were developed in the 1970s, having been derived from the chemical structure of fentanyl—a drug that today is notorious for its role in the ongoing opioid crisis in the United States. Carfentanil, however, is about 100 times more potent than fentanyl, whereas sufentanil, which is used in controlled clinical settings, is 5 to 10 times more potent. Fentanyl itself is 50 to 100 times stronger than morphine.

Carfentanil was introduced in 1986 for use as a general anesthetic in large mammals, having been sold under the brand name Wildnil until 2003. Today, outside of illicit production, it is available only in a specific quantity and concentration for veterinary use. It is extremely potent: 2 mg, which is sufficient to sedate an elephant, is enough to cause fatal overdose in several dozen humans. Meanwhile, sufentanil frequently is employed to treat pain following surgical operations, when strong, short-acting pain relief is required.

Both carfentanil and sufentanil are controlled substances. However, illegally manufactured forms of these and other fentanyl-related agents are often found in the illicit drug supply, frequently mixed with other substances, including heroin or cocaine. This typically occurs without the user’s knowledge, which has contributed significantly to opioid overdose and deaths from opioid use.

Kara Rogers