> Western Medicines > Fentanyl


Used for: Severe ongoing pain, Pain relief
Chinese name:

What is Fentanyl for?

Fentanyl belongs to a class of medications called opioid analgesics. It works by inhibiting nerve signal transmission of pain in the brain and nervous system. It is a powerful analgesic and is used for severe pain management, for example in chronic pain management for cancer patients. Fentanyl is not used for mild and short-term pain.

How to use it?

Fentanyl transdermal patches are often used, while it is also available in nasal spray and buccal tablets. The dosage regimen is individualized based on pain severity and response to therapy by the doctor. Fentanyl is used as needed to treat breakthrough pain but not more often than four times daily.


Apply Fentanyl transdermal patches to the skin as directed by your doctor. Select a dry, non-hairy area on a flat part of the body, such as the chest, sides, back or upper arms. Change the patch every 72 hours and apply to a different area each time to avoid irritation. Avoid applying the medication on open wounds. Avoid exposing the application site to heat as it affects drug absorption. Fold the patch in half and discard it properly as a used patch still contains enough Fentanyl to cause serious harm.

What are the side effects of Fentanyl?

Common side effects of Fentanyl include constipation, dizziness and drowsiness, dry mouth, euphoric mood, flushing, hallucinations, nausea and vomiting (more common on initiation), and respiration depression (with high dose). Mild irritation, itching or redness may occur at the application site. Like all opioid medications, people can become tolerant or addicted to Fentanyl, which can result in withdrawal symptoms when you try to stop the medicine.

Who should not take Fentanyl?

  • People who are allergic to Fentanyl or any component of the formulation.
  • People with a history of alcohol or drug dependence.
  • Patients with respiratory depression, serious bronchial asthma or gastrointestinal obstruction.
  • People who are taking or took monoamine oxidase inhibitors (MAOIs) within the past 14 days.

Pharmacist Tips:

  • Note that opioids have the potential to be addictive and you can become tolerant over time.
  • Tell your doctor if you experience severe side effects, such as difficulty breathing.
  • Do not stop the medication abruptly if you have used Fentanyl over long periods of time.
  • Eat more high-fibre foods, drink more water and do more exercise to reduce the side effect of constipation.
  • It is best to avoid alcohol while taking Fentanyl.

Common dosing schedule:
Fentanyl transdermal patches should be changed every 72 hours. Your doctor will regularly check to see if the dosage should be adjusted based on your level of pain.


Your doctor will not increase your dosage sooner than 3 days after the first dose and may increase your dosage every 6 days.


Some common medications Fentanyl may interact with:

Please notify your doctor or pharmacist if you are taking the above medication, dosage adjustments might be needed.

Where to buy Fentanyl in Hong Kong?

In Hong Kong, Fentanyl is a prescription only medicine, and requires a prescription from a doctor to be purchased in a pharmacy. It can also be obtained from doctors. To find a pharmacy near you, refer to the list of pharmacies (“Authorized Sellers of Poisons”) from the Hong Kong Department of Health.


For more information about drug names and ingredients, you can visit Hong Kong’s Drug Office at https://www.drugoffice.gov.hk

Need more information?

For detailed information about the use of Fentanyl in children, pregnancy and breastfeeding, and for questions about drug interactions, please check with your pharmacist or doctor.

Disclaimer: our goal is to provide you with the most relevant drug information and common dosage for Hong Kong. This information does not constitute medical advice. For specific treatment recommendations and advice, always discuss with your doctor or pharmacist, and follow the instructions included with your specific medicine.

Brands in Hong Kong
Available dosage
  • 400mcg / 600mcg / 800mcg (Buccal Tablets)
  • 0.05mg/ml (Injections)
  • 100mcg / 400mcg (Nasal Spray)
  • 12mcg/h / 25mcg/h / 50mcg/h (Transdermal Patches)
Drug class
Sub class
Opioid Analgesics
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