What Is A Lethal Dose Of Fentanyl?

Medically Reviewed by Johnelle Smith, M.D on July 5, 2021

Fentanyl is a very strong opioid drug. It is available by prescription and also manufactured illicitly. Fentanyl can be toxic and potentially lethal when taken in ways other than prescribed by a doctor.

Fentanyl Lethal Dose | How Much Fentanyl Is Too Much?

Fentanyl is a very powerful opioid drug that can have fatal consequences if it is taken in very high doses (about 2 milligrams or more) or mixed with other drugs.

When taken as prescribed, fentanyl can be effective for its intended use. Do not take fentanyl in any way other than prescribed. Taking illegally manufactured fentanyl can be dangerous.

Do not use this information to determine a safe drug dosage. If you suspect someone has overdosed on fentanyl, call 911 or your local poison control center right away.

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Learn more about the lethal doses of commonly abused drugs

Lethal Dose Of Fentanyl

The estimated lethal dose of fentanyl is about 2 milligrams (mg). Depending on where the fentanyl comes from (i.e. illicit or prescription), the lethal dose may be lower.

Two milligrams of fentanyl is equal to about 0.002 grams. This is a much smaller lethal dose compared to heroin, which can be fatal at 30 mg to 500 mg.

What Can Cause Fatal Fentanyl Overdose?

A fentanyl overdose can be fatal or non-fatal. There are several ways that a person can fatally overdose on fentanyl.

Causes of fatal fentanyl overdose can include:

  • taking illicit forms of fentanyl
  • taking heroin laced with fentanyl
  • taking stimulants mixed with fentanyl (e.g. cocaine)
  • taking higher doses than prescribed
  • taking doses more often than prescribed
  • crushing and snorting tablets
  • injecting fentanyl
  • mixing fentanyl with other drugs (including alcohol)

Illicit forms of fentanyl are often cut with illicit drugs like heroin, cocaine, MDMA, and methamphetamine. Not everyone who buys these drugs is aware they are laced with fentanyl.

If someone is showing signs of opioid overdose after taking illicit drugs, call 911 and administer naloxone by injection or with nasal spray right away.

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Signs Of Fentanyl Overdose

Overdose can be reversed with quick treatment. If someone is showing the following signs of overdose, call for emergency medical assistance right away.

Signs of fentanyl overdose can include:

  • slow, shallow, or no breathing
  • difficulty breathing
  • dizziness
  • very weak pulse
  • cold, clammy skin
  • bluish fingernails and lips
  • gurgling noises
  • tiny pupils
  • confusion
  • unable to respond
  • unconsciousness

What To Do If Someone Has Overdosed On Fentanyl

Not all overdoses are fatal. If you suspect someone has overdosed on fentanyl, call for emergency medical assistance right away.

People who have overdosed on fentanyl will likely be unresponsive and may not be breathing.

In the meantime, if you have naloxone (Narcan) on hand, administer that right away.

Naloxone can block the effects of opioids in the brain. This can reverse an overdose when administered quickly. Without treatment, severe cases of overdose can be fatal.

Finding Treatment For Opioid Addiction

Opioid overdose can be a sign of drug misuse and addiction. If you or a loved one has overdosed on fentanyl or is using fentanyl, seeking substance abuse treatment is highly recommended.

By calling our helpline, we can:

  • identify your treatment options
  • verify your insurance (as applicable)
  • find an opioid addiction treatment program that’s right for you

You are not alone. Call us today to find an opioid addiction treatment program that’s right for you or a loved one in your life.

This page does not provide medical advice. See more

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Medically Reviewed by
Johnelle Smith, M.D on July 5, 2021
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