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What Is a Lethal Dose of Fentanyl?

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Fentanyl is a synthetic opioid made from chemicals manufactured from the opium poppy plant.  Fentanyl and other synthetic drugs are the most commonly involved in overdose deaths. Even in small doses, it can be deadly. Over 150 people die daily from overdoses related to synthetic opioids like fentanyl.

Fentanyl deaths are on the rise. 100,000 people died from a drug overdose in 2021, and fentanyl was responsible for more than 60%. That same year, there were almost 123,000 fentanyl-related emergency department visits. Those numbers reveal a significant increase over the past several years.

Producing illegal fentanyl is not an exact science.  Two milligrams of fentanyl can be lethal depending on a person’s body size, tolerance, and past usage.  DEA analysis has found pills ranging from .02 to 5.1 milligrams (more than twice the lethal dose) of fentanyl per tablet.

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

Someone can take a pill without knowing it contains fentanyl. It is also possible to take a pill knowing it has fentanyl but without knowing if it contains a lethal dose.

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Lethal Dose of Fentanyl Compared to Commonly Abused Drugs

The lethal dose for a given drug may not be the same for everyone. While lethal dosage amounts are average estimates, several factors may affect this. Factors influencing a lethal dose include age, weight, drug tolerance, history of drug use, medical history, use of multiple drugs, purity level, and type of drug administration.

Commonly Used Illicit Drugs: 

  • Illicit fentanyl.
  • Cocaine.
  • Heroin.
  • Methamphetamine.
  • Marijuana.
  • Fentanyl– Two milligrams of fentanyl can be lethal depending on a person’s body size, tolerance, and past usage.
  • Cocaine– is a powerful stimulant that can be lethal in doses exceeding 1.2 g on average. In people with high sensitivity to cocaine, a fatal overdose may occur with doses over 30 mg.
  • People who use cocaine regularly and in high doses may have a higher tolerance for cocaine. This means the fatal amount for them may be higher than for the average person.
  • Heroin– is an illicit opioid drug. It is commonly cut with other substances, affecting its purity and lethal dosage. The estimated lethal dose of heroin is 200 mg, but people with heroin use disorder may be able to tolerate 10 times as much. Heroin is sometimes cut with fentanyl, which can increase the overdose risk.
  • Methamphetamine– is an addictive stimulant. The estimated lethal dose of methamphetamine is about 200 mg or 0.15 to 0.2 g.

THC– is the active ingredient in cannabis or marijuana. Marijuana is considered one of the least toxic of all recreational drugs. There is no known amount of THC found to be lethal.

What Quantity of Fentanyl Is Required to Feel Its Effects?

There is a difference between what is legally prescribed for users to feel the effects of fentanyl and how much fentanyl a person may ingest when using illicitly manufactured fentanyl.

Pharmaceutical fentanyl comes in an injectable form of 50 mcg. Dosing is as follows by indication, 50-100 mcg, and consideration is given to patients 65 and older due to increased adverse side effects.

There is no way to identify how much fentanyl may be found in illicitly produced fentanyl.

DEA analysis has found pills ranging from .02 to 5.1 milligrams (more than twice the lethal dose) of fentanyl per tablet.

Someone can take a pill without knowing it contains fentanyl. It is also possible to take a pill knowing it has fentanyl but without knowing if it contains a lethal dose.

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Does Method of Use & Form of Fentanyl Affect Lethality?

Fentanyl is from a group of drugs called opioids or narcotics. It works in the central nervous system and the brain to block pain signals to the rest of the body. It also reduces the anxiety and stress caused by pain. A fentanyl injection into a vein gives the quickest pain relief. It works almost immediately and is usually only administered in the hospital.

Fast-acting fentanyl tablets, lozenges, and nasal sprays take 15 to 30 minutes to work but wear off after 4 to 6 hours.

Fentanyl patches can take up to a day or two to start working, but they will last longer. Patches are usually given after fentanyl tablets. This is to ensure you have pain relief from the pills until the patches start to work.

Fentanyl and other synthetic opioids are the most common drugs involved in overdose deaths. Even in small doses, it can be deadly.

Fentanyl may cause severe breathing problems or death if used by people not being treated with other narcotic medications or who are not tolerant to narcotic drugs.

Percentage of Counterfeit Pills That Contain Lethal Doses

According to the DEA, 4 out of every 10 counterfeit pills with fentanyl contain a lethal dose. One of the most dangerous things about fentanyl is that it can be indistinguishable from other pills or drugs a person may think they are using. Drug dealers are known to press fentanyl into pills that look identical to other medications, such as oxycodone (Oxycontin, Percocet), hydrocodone (Vicodin), and alprazolam (Xanax), or stimulants like amphetamines (Adderall).

People may think they have a typical pain medication or stimulant, but they are ingesting a drug 100x more potent than morphine.

Symptoms Associated With Fentanyl Overdoses

Overdose of fentanyl is extremely dangerous. If you believe someone is overdosing on fentanyl or any other drug, call 911 immediately.

Symptoms of Fentanyl Overdose: 

  • Constricted pupils.
  • Severe respiratory depression, such as slow or shallow breathing.
  • Cold, clammy skin.
  • Gray, blue, or pale skin.
  • Blue or purple lips and nails.
  • Respiratory arrest, or altogether stopped breathing.
  • Extreme decreases in the level of consciousness.
  • Limp or flimsy arms and legs.
  • Slurred speech or inability to speak.
  • Loss of consciousness.
  • Unresponsiveness.
  • Vomiting.
  • Choking or gurgling sounds.

Accidental Overdose Rates Due to Unknown Fentanyl Presence

As previously mentioned, there have been 100,000 overdose deaths in the United States involving opioids, and it is believed that 60% of those deaths involve fentanyl. According to the DEA, they seized over two hundred million counterfeit pills laced with fentanyl in 2021. This is more fentanyl seized than in the past two years combined.

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At Guardian Recovery, we remain dedicated to providing our clients with a comprehensive program of fentanyl detox — one that focuses on much more than physical stabilization. In addition to emphasizing physical recovery, we tackle mental, emotional, and spiritual well-being. While prioritizing a safe and pain-free cocaine withdrawal, we offer individualgroup, and family therapy sessions, case management services, relapse prevention training, and aftercare planning.

Contact us today if you or your loved one is ready to begin an entirely new way of life and commit to long-term recovery. As soon as you call, we start developing a plan of action that begins with an initial pre-assessment. This assessment helps us determine the most appropriate level of care for each unique case. We identify potential coverage options if our medically monitored detox program is a good fit. We work closely with most major regional and national insurance providers. Contact us today for a free, no-obligation insurance benefit check.


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Disclaimer: Does not guarantee specific treatment outcomes, as individual results may vary. Our services are not a substitute for professional medical advice or diagnosis; please consult a qualified healthcare provider for such matters.


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Reviewed professionally for accuracy by:

Ryan Soave


Ryan Soave brings deep experience as a Licensed Mental Health Counselor, certified trauma therapist, program developer, and research consultant for Huberman Lab at Stanford University Department of Neurobiology. Post-graduation from Wake Forest University, Ryan quickly discovered his acumen for the business world. After almost a decade of successful entrepreneurship and world traveling, he encountered a wave of personal and spiritual challenges; he felt a calling for something more. Ryan returned to school and completed his Master’s Degree in Mental Health Counseling. When he started working with those suffering from addiction and PTSD, he found his passion. He has never looked back.

Written by:

Cayla Clark

Cayla Clark

Cayla Clark grew up in Santa Barbara, CA and graduated from UCLA with a degree in playwriting. Since then she has been writing on addiction recovery and psychology full-time, and has found a home as part of the Guardian Recovery team.

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