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Fentanyl vs. Heroin | Comparing These Powerful Opioids

Peter Manza, PhD profile image
Reviewed By Peter Manza, PhD • Updated Oct 29, 2023 • 7 cited sources

Fentanyl and heroin are both potent opioids. Heroin is commonly sold as white or brown powder, while fentanyl resembles heroin but comes as white, tan or gray powders and sometimes in pill form. 

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Both drugs are often injected, but heroin can also be snorted or smoked. Both pose risks of overdose, respiratory depression, infectious diseases from shared needles and legal issues. While both heroin and fentanyl can trigger fatal opioid overdose, fentanyl is responsible for the majority of these deaths.[1] 

Breakdown of Fentanyl vs. Heroin

Type of DrugOpioidOpioid
Visual DifferencesTypically appears as a white or brown powder or black sticky substance (black tar heroin)Can resemble heroin, but may be white, tan, or gray; often found in pill form or mixed with other drugs
Ways to ConsumeInjected, snorted, smokedPatches or lozenges (prescription) and via injection (illicitly)
Change in Brain ChemistryBinds to opioid receptors, increasing dopamine, leading to intense pleasure, pain relief and risk of respiratory depressionBinds to opioid receptors, alters pain perception, produces euphoria and increases risk of respiratory depression
Physical Effects Euphoria, relaxation, warm flushing of the skin, slowed breathing and constricted pupilsEuphoria, sedation, drowsiness, respiratory depression and constricted pupils
Mental Effects Intense pleasure, reduced anxiety, cloudy thinking and drowsinessIntense euphoria, altered perception and impaired cognition
RisksOverdose, respiratory depression, infectious diseases from shared needles, collapsed veins and legal issues related to possession and useAccidental overdose due to potency, respiratory depression, risk of counterfeit drugs, infectious diseases from shared needles and legal issues related to possession and use
Addictive PotentialHighly addictive, with rapid development of physical and psychological dependenceHighly addictive, with rapid development of physical and psychological dependence
Overdose Deaths per Year9,173 in the U.S. in 202170,601 in the U.S. in 2021 due to synthetic opioids, which were primarily due to fentanyl
Sources: [1-4]

Fentanyl Side Effects

Not everyone will experience the same effects when they take fentanyl due to variations in physiology and the chemical makeup of the compound, but some common side effects of fentanyl include the following:[1]

  • Nausea and vomiting
  • Constipation
  • Dizziness or lightheadedness
  • Sleepiness or drowsiness
  • Confusion or cognitive impairment
  • Headache
  • Dry mouth
  • Sweating
  • Itching or rash
  • Respiratory depression (slowed breathing)
  • Hypotension (low blood pressure)
  • Urinary retention
  • Muscle stiffness or spasms
  • Difficulty swallowing
  • Changes in mood or mental health, such as anxiety or depression
  • Decreased appetite
  • Weakness or fatigue
  • Tolerance (needing higher doses for the same effect)
  • Physical dependence and withdrawal symptoms upon discontinuation of fentanyl

Most people do not use fentanyl on its own unless they have a severe opioid use disorder (OUD). 

Many people take fentanyl inadvertently, as it is often used to cut heroin and make it more potent. They take their “usual” dose of heroin only to find that it is far stronger than expected because it contains some amount of fentanyl. This often leads to fatal overdose.

Heroin Side Effects

Similarly, not everyone experiences the exact same thing when they use heroin, but in general, some common side effects of heroin use include the following:[2]

  • Euphoria and intense pleasure
  • Drowsiness or sedation
  • Nausea and vomiting
  • Itchy skin or flushed appearance
  • Dry mouth
  • Constricted (pinpoint) pupils
  • Slowed breathing
  • Hypotension (low blood pressure)
  • Slow heart rate
  • Constipation
  • Confusion or clouded thinking
  • Impaired coordination
  • Memory problems
  • Sexual dysfunction
  • Weakened immune system
  • Increased risk of infectious diseases, such as HIV or hepatitis, due to shared needles
  • Collapsed veins (from injection use)
  • Track marks (scarring and bruising) at injection sites
  • Abscesses or skin infections
  • Respiratory depression, which can be life-threatening
  • Overdose, potentially leading to coma or death

Heroin use can have substantial long-term effects on both physical and mental health, including increased tolerance to the drug, the development of OUD and withdrawal symptoms that occur when levels of heroin or other opioids drop in the system for any reason. 

Additionally, heroin use can cause significant social, financial and legal problems due to its illegal status and the compulsive behaviors that often characterizes psychological addiction to the drug.

Comparison of the Risks of Fentanyl vs. Heroin

Fentanyl and heroin are both powerful opioids. As a result, their legal status and potential risks are similar even though their potency is quite different. 

Here is a brief outline of each substance’s risks:


  • Potency: Fentanyl is an extremely potent synthetic opioid, estimated to be 50 to 100 times stronger than morphine and about 50 times stronger than heroin.[5] Due to this strength, very small doses can trigger overdose.
  • Accidental overdose risk: Due to its potency, accidental overdose risks are high when individuals take fentanyl mixed with other drugs or miscalculate the dose.
  • Rapid onset and short duration: Fentanyl acts rapidly but wears off rapidly as well, increasing the likelihood of overlapping doses and overdose.
  • Medical uses: Fentanyl is widely prescribed by healthcare professionals for severe pain management in a hospital or hospice setting, though illicitly produced fentanyl often makes its way into the black market.


  • Potency: Heroin is a semisynthetic opioid derived from morphine that can vary considerably in potency depending on its source, leading to unpredictable effects.
  • Overdose risk: Heroin use poses a substantial overdose risk, especially when taken in higher doses or mixed with the use of other substances like fentanyl.
  • Heroin injection risks: Heroin injection carries additional risks, such as potential for infections, collapsed veins and the potential transmission of blood-borne diseases through shared needles.[6]
  • Legal status: Heroin is illegal in most countries and associated with criminal activities for its production and distribution.[6] In the U.S., it is not legal for any use, including medical treatment. 

Is One Worse Than the Other?

While both fentanyl and heroin are dangerous and addictive opioids, fentanyl stands out as an especially risky drug due to its powerful effects. Even small amounts of fentanyl can produce life-threatening outcomes.[7]

The truth is, however, that use of either drug can have devastating consequences. Opioid use disorder related to either heroin or fentanyl use, or both, is treatable with Medication for Addiction Treatment (MAT) programs. 

Getting Started With Bicycle Health

While heroin and fentanyl are both highly addictive, Bicycle Health offers a comprehensive treatment option that can help people put their risk of overdose and other life-changing consequences of OUD in the past. 

At Bicycle Health, we offer MAT via Suboxone and therapy in a program that combines medical expertise, counseling and personalized support to help patients on their journey to recovery. Through our telehealth platform, we make these services available to everyone. 

Call now to learn more about whether or not our program is a good fit for your needs. You can change your life starting today.

Reviewed By Peter Manza, PhD

Peter Manza, PhD received his BA in Psychology and Biology from the University of Rochester and his PhD in Integrative Neuroscience at Stony Brook University. He is currently working as a research scientist in Washington, DC. His research focuses on the role ... Read More

  1. Drug Fact Sheet: Fentanyl. Drug Enforcement Administration. Published April 2020. Accessed July 26, 2023.
  2. Heroin DrugFacts. National Institute on Drug Abuse. Published December 16, 2022 Accessed July 26, 2023.
  3. Gladden RM, Martinez P, Seth P. Fentanyl law enforcement submissions and increases in synthetic opioid-involved overdose deaths – 27 states, 2013-2014. Morbidity and Mortality Weekly Report. 2016;65(33):837-843. doi:10.15585/mmwr.mm6533a2 
  4. Drug overdose death rates. National Institute on Drug Abuse. Published June 2023. Accessed July 26, 2023. 
  5. Fentanyl facts. Centers for Disease Control and Prevention. Published June 27, 2023. Accessed July 26, 2023.
  6. Heroin fast facts. National Drug Intelligence Center. Published March 2003. Accessed July 26, 2023.
  7. Opioid facts. U.S. Department of Justice. Published November 28, 2022. Accessed July 26, 2023.

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