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Why is fentanyl so dangerous?

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on Aug 15, 2022.

Official answer


Key takeaways:

  • When fentanyl is abused or taken in an overdose, this opioid can quickly be fatal because it is so potent and people are not used to its effects.
  • There is a significant risk that any illegal drug you buy on the streets, buy online, or that may be given to you is intentionally contaminated with fentanyl. Fentanyl is often consumed unknowingly by users of street drugs leading to death.
  • When it's used in combination with other central nervous system depressants like opioids, alcohol or benzodiazepines, the risk of overdose and death multiplies.

There is no way to know how much illicit fentanyl may be contained in a drug you plan to use or how potent it is. However, fentanyl test strips are available at certain health departments or syringe exchange programs, so you can test the drug you plan to use for fentanyl. Ask your healthcare provider where you can get these strips.

Another reason fentanyl is so dangerous is that many people are simply unaware of this ongoing threat. According to the CDC, man-made opioids like fentanyl are fueling the majority of overdose deaths in the United States.

Even though an online pill identifier might show that a pill bought on the street looks like a legitimate prescription pill because it has the same color, shape or imprint code, this is most likely NOT true. Illegal drug manufacturers create fake opioid pills to look exactly like the real ones. The fake pills may also contain fentanyl, or only contain fentanyl. You cannot tell if a pill, powder, nasal spray or injection bought off of the street contains a deadly dose of any drug just by looking at it.

Opioids were involved in 68,630 overdose deaths in 2020 (74.8% of all drug overdose deaths).

  • In 2020, there were 56,000 overdose deaths due to synthetic opioids like fentanyl. These deaths rose by over 56% compared to 2019 and accounted for more than 82% of all opioid deaths.
  • Adulterated drugs bought on the streets or online are often laced with fentanyl leading to overdose deaths. Because of its potency and low cost, drug dealers have been mixing fentanyl with other drugs including heroin, methamphetamine, counterfeit pills, cocaine, or crack, increasing the likelihood of a fatal interaction.
  • There is no official quality control with illegal manufacturers, and fake pills or other drugs often contain lethal doses of fentanyl. Unless the illegal drug is tested in a laboratory, there’s no way to know how much fentanyl it contains.
  • Illegally made fentanyl smuggled into the U.S. often originates from Mexico, China, and increasingly, India, according to the DEA.

Is fentanyl legal?

Yes, fentanyl is classified as a Schedule II controlled substance in the U.S. and is available by prescription only. When monitored and used as directed by your physician, it can effectively relieve severe pain. You should never use it unless it has been prescribed by a licensed medical professional who cares for you and is dispensed by a licensed pharmacy.

Legal fentanyl is a synthetic opioid medicine typically used to treat patients with long-lasting severe pain or severe pain following surgery. It is similar to morphine but about 100 times more potent. For control of cancer pain, fentanyl is only given to patients who are “opioid-tolerant”, meaning they are used to the narcotic effects of fentanyl and have already been taking around-the-clock opioids for severe cancer pain.

How much fentanyl can kill you?

One 2 milligram (mg) dose of fentanyl is enough to kill an adult, but may be more or less depending upon your body size, opioid tolerance, and former usage. Fentanyl can kill you within a matter of 2 minutes, usually due to respiratory failure (breathing that has stopped).

Fatal dosage for fentanyl

Source: DEA, 2022. Two milligrams of fentanyl can be a lethal dose in most people, according to the DEA.

Prescription fentanyl is dosed in micrograms, designated by the abbreviation “mcg”. This is an extremely small dose. Most other drugs are dosed in milligrams ("mg") -- for example, 500 mg of acetaminophen (Tylenol) or 25 mg of diphenhydramine (Benadryl).

According to the DEA, 42% of pills they tested for fentanyl contained at least 2 mg of fentanyl, a potentially lethal dose. Drug traffickers typically distribute fentanyl by the kilogram. One kilogram of fentanyl has the potential to kill 500,000 people.

How does fentanyl kill you?

Most people die from respiratory depression and failure from an overdose of an opioid like fentanyl. This means breathing stops altogether, and they cannot get the oxygen their brain and body need to survive. Some people may also vomit and choke to death because they are unconscious. This typically occurs rapidly, in a matter of a few minutes.

A fentanyl overdose may lead to:

  • stupor (dazed or nearly unconscious)
  • pinpoint-sized pupils
  • cold and clammy skin
  • cyanosis - blue discoloration of the skin, lips or fingernails
  • coma (unconscious, unable to awaken)
  • respiratory depression and failure leading
  • death

If administered in time and in a sufficient dose (or doses), the opioid antidote naloxone (Narcan) may be able to reverse a fentanyl overdose and respiratory depression.

You can access naloxone from most pharmacists in the U.S. without a prescription. If you, a family member, or a friend take illegal drugs, it is important to have immediate access to naloxone to help possibly save a life. Ask your healthcare provider for more information.

Learn more: Know Your Naloxone: Save a Life

For more information, you can contact find evidence-based treatment and service options near you by visiting or by calling the 24/7, National Helpline at 800-662-HELP (4357).

This is not all the information you need to know about fentanyl and does not take the place of your healthcare provider's advice. Discuss this information and any questions you have with your doctor or other health care provider.


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