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What Does Fentanyl Do To Your Body?



Medically Reviewed by Dr. Mohammed Saeed, MD.

Fentanyl is an opioid, often prescribed by doctors to control serious chronic pain. Because fentanyl can have severe, even life-threatening side effects, it is not usually prescribed unless other remedies have failed. It’s most often used to treat pain experienced by cancer patients, and for those for whom other opioids are no longer effective. Fentanyl users are at high risk for abuse and dependence and must be closely monitored by medical professionals.

How Do Opioids Affect the Brain?

As with other opioid drugs, fentanyl affects the opioid centers of the brain, altering how your body experiences pain. It affects how pain messages are sent throughout the body, both throughout the spinal cord and the central nervous system. Even though fentanyl mimics natural opioids in the body, its effects are much stronger.

The purpose of the body’s natural opioids is to trigger feelings in the body of relaxation and well-being. Opioids also control the pleasure and reward center of the brain. Opioids do this by causing a rush of dopamine – the feel-good hormone – throughout the body. Fentanyl, and other opioid drugs, trigger these pleasure reactions at much more intense levels than would happen naturally. Repeated use of opioids makes the brain less sensitive to their presence, so more is needed to achieve the desired effect, leading to dependence and abuse.

What are the Physical Effects of Fentanyl?

Although fentanyl is effective at relieving pain, the side effects can be life-threatening. Fentanyl users are at increased risk of respiratory depression, causing slow, shallow breathing, which can be fatal.

Fentanyl abuse is often characterized by euphoria, drowsiness, and lethargy, and can include many other symptoms, some quite severe. The following side effects can occur even when the drug is used as prescribed:

  • Headache
  • Dry mouth
  • Extreme fatigue
  • Weakness
  • Confusion]
  • Dizziness, feeling light headed
  • Flushing
  • Trouble concentrating
  • Vision Problems – constricted pupils, difficulty seeing
  • Stiff or rigid muscles
  • Urine retention
  • Severe Constipation
  • Itching or hives
  • Nausea and vomiting
  • Appetite loss
  • Weight loss
  • Insomnia, bad dreams
  • Depression
  • Hallucinations
  • Sweating, often while sleeping
  • Shaking
  • Swollen or inflamed arms and legs

According to the Centers for Disease Control and Prevention (CDC), over 70,000 drug overdose deaths were reported in 2017. Synthetic opioids were responsible for 67.8% of those deaths.


Dr. Mohammed Saeed, MD.

Dr. Saeed is a psychiatry specialist with over 40 years of experience in the medical field. He received training in General Psychiatry at the University of Texas Medical Branch, where he was selected as the Medical Director of the Division of Child and Adolescent Psychiatry. He currently serves as the medical director at Into Action Recovery Centers. Full Bio

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