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Side Effects of Fentanyl (Duragesic, Subsys, Actiq)


Side Effects of Fentanyl (Subsys)

Fentanyl, available under the brands Duragesic, Subsys, Actiq, is part of the narcotic analgesics class. Subsys is an opioid medication for severe pain in cancer treatment. The actions of Subsys take place in the central nervous system (CNS). It is also used as part of anesthesia to prevent pain after surgery or other medical procedures.

Subsys Abuse and Dependence

According to the FDA, Subsys can lead to potential drug dependence and addiction. Significant dependence on Subsys does not occur until a few weeks of treatment. Long-term use of Subsys should not be discouraged if it is used to relieve continuous pain. Physical dependence of Subsys should not be suddenly stopped, as it may result in withdrawal symptoms. Withdrawal side effect symptoms can be prevented by gradually reducing the dosage over a period of time.

Warnings Before Taking Subsys

The FDA. advises precautions before undergoing Subsys. There are few important safety considerations with Subsys use: it can slow or stop your breathing, cause addiction, overdose or death. This is particularly dangerous for users who are not prescribed the medication, especially someone with a history of drug abuse.


Do not use Subsys if you have known allergy to the medication or if you have severe breathing problems such as asthma attacks or a blockage in your digestive tract (stomach or intestines). Drinking alcohol, using prescription or over-the-counter medicines that contain alcohol, should be avoided with Subsys because it can lead to overdose and death.


Caution is to be taken if you have any type of liver or kidney disease, mental illness, alcoholism or drug addiction, urination problems, or problems with your gallbladder, pancreas, or thyroid. Additionally, some medicines can interact with Subsys and cause a serious condition known as serotonin syndrome.


Make sure to discuss with your healthcare provider if you also take medicine for depression, migraine headaches, serious infections, or prevention of nausea and vomiting. In addition, medicines, certain antibiotics, antifungal medications, heart and blood pressure medications, and HIV and AIDS medications can cause unwanted or dangerous effects when used with Subsys.

Common Side Effects

Side effects of Subsys are:


  • Constipation (which may be severe)
  • Nausea
  • Sleepiness
  • Vomiting
  • Tiredness
  • Headache
  • Dizziness


(Subsys label reported by the FDA).


Immediately contact your healthcare provider if you are experiencing difficulty in breathing, tachycardia (abnormally fast heart rate), chest pain, swelling in the face, tongue or throat, extreme drowsiness, light-headedness when changing body positions, or fainting.

About Pharmacogenetic Testing

In 2009, almost 50% of all drug related hospitalizations were due to severe reactions to medications in comparison to 21.1% from illicit drugs. It has become a growing problem and pharmacogenetics aims to alleviate that dilemma.


One of the reasons that medication hospitalizations occur is due to genetic differences between people. The variations means that people handle medications differently from each other. Pharmacogenetics examines those differences and relays that information to doctors. Doctors will use that information to prescribe appropriate medications.

Know Your Risk for Side Effects with the Rxight® Genetic Test

Rxight® genetic testing sequences a panel of genes and their alleles to analyze inter-individual differences in pharmacogenetic response to Subsys, along with hundreds of other common prescription and over-the-counter (OTC) pharmaceutical agents. It allows individuals and prescribers to know if Subsys is “red-flagged” for them as a medication that could result in dangerous and potentially life-threatening reactions.


Call us to learn more about the Rxight® genetic test, at 1-888-888-1932 or email us at support@Rxight.com.


Contributors to this Article:
Michael Sapko, MD, PhD; and Deborah Kallick, PhD, Medicinal Chemistry

Read more about Rxight® : What is Pharmacogenetics?