Fentanyl is a very strong opioid painkiller. In South Africa it is Schedule 6 — the most tightly controlled category — and it is used as an injection in hospitals for anaesthesia and severe pain, and as a skin patch for constant severe pain, usually in cancer or palliative care. It is not a medicine for ordinary pain.
What is Fentanyl?
The South African Medicine Price Registry lists fentanyl in two forms, all Schedule 6:
| Type | Products | Strengths |
|---|---|---|
| Injection | Sublimaze, Fentanyl-Fresenius, Pharma-Q Fentanyl | 50 mcg/ml; 100 mcg/2 ml; 500 mcg/10 ml |
| Skin patch | Durogesic, Adco Tenyl, Fendermal | 12, 25 and 50 mcg per hour |
Note the units. Fentanyl is measured in micrograms — thousandths of a milligram — where morphine is measured in milligrams. It is roughly a hundred times more potent than morphine, and that fact governs everything about how it is handled. A quantity that would be trivial for most medicines is a full dose here.
Fentanyl acts on mu opioid receptors in the brain and spinal cord, blocking pain signals and altering the emotional response to pain. It is fat-soluble, which lets it cross into the brain very quickly by injection and lets it pass through skin steadily from a patch.
The two forms behave completely differently:
The injection acts within minutes and wears off quickly. It is used by anaesthetists during surgery and in intensive care and emergency settings, always with monitoring and equipment to support breathing.
The patch delivers a steady dose through the skin over about three days. It takes 12 to 24 hours to reach full effect after the first patch, and levels keep falling for a long time after one is removed, because a reservoir builds up in the skin and fat. That slow behaviour in both directions is the source of most patch-related accidents.
What is Fentanyl commonly used for?
The injection:
- General anaesthesia — as part of the anaesthetic during surgery.
- Severe acute pain in emergency and intensive care.
- Procedural sedation, and pain relief in ventilated patients.
The patch:
- Constant severe pain that needs round-the-clock opioid treatment and cannot be managed with weaker medicines — most often advanced cancer pain.
- Palliative care, where the patch is valuable because it works without swallowing, which matters a great deal when someone cannot take tablets.
- Severe chronic pain, in carefully selected patients under specialist care.
Patches are for people already established on regular opioids — “opioid-tolerant” patients. Applying a fentanyl patch to someone who has not been taking opioids regularly can stop their breathing. This is not a theoretical caution; it is the main way people die from prescribed fentanyl.
Fentanyl is not for short-term, occasional or mild-to-moderate pain, for headaches, for backache, or for pain after minor procedures. For those, paracetamol, anti-inflammatories or weaker opioids are appropriate.
A separate warning belongs on any page about this medicine. Illicitly manufactured fentanyl is now a major cause of overdose deaths worldwide. It is mixed into counterfeit tablets and other street drugs, frequently without the buyer’s knowledge, and the amounts involved are impossible to judge by eye. Any “pill” not dispensed by a pharmacy may contain it. Nothing on this page applies to such products, and no amount of caution makes them safe.
How Fentanyl fits into this medicine category
| Step | Examples | Where it fits |
|---|---|---|
| Simple analgesics | Paracetamol | Mild pain and fever |
| Anti-inflammatories | Diclofenac (K-Fenak OTC), ibuprofen | Pain with inflammation |
| Weak opioids | Codeine, tramadol | Moderate pain |
| Strong opioids | Morphine, oxycodone | Severe pain |
| Very potent opioids | Fentanyl | Severe pain and anaesthesia; specialist use only |
| Compound remedies | HP553 and similar | Everyday symptomatic relief |
Fentanyl sits at the far end, and it belongs there. See the general medicines hub.
What to check before using Fentanyl
If a patch has been prescribed, the practical rules matter as much as the dose.
- Never cut a patch. Cutting can release the whole reservoir at once.
- Apply to clean, dry, unbroken, hair-free skin on the upper body, and press it in place for the time stated. Rotate the site each time.
- Keep heat away from the patch. Hot baths, saunas, electric blankets, heat pads, direct sun and fever all increase absorption, sometimes dangerously. If you develop a high fever, tell your doctor.
- Remove the old patch when you apply a new one, and check daily that it is still stuck and that only one is on.
- Dispose of used patches carefully — fold sticky sides together and return them to the pharmacy. A used patch still contains a substantial amount of drug, and children and pets have been seriously harmed by discarded ones.
- Store patches securely, out of sight and reach of children. Skin contact alone can be enough to harm a child.
- Never give it to anyone else. A dose that is routine for a tolerant patient can be fatal for someone who is not.
Tell your doctor if you:
- Have breathing problems — COPD, asthma, sleep apnoea.
- Take benzodiazepines, sleeping tablets, sedating antihistamines, gabapentin or pregabalin, or drink alcohol. Combining these with an opioid is a leading cause of fatal respiratory depression.
- Take antidepressants, triptans, or medicines affecting liver enzymes such as ritonavir, ketoconazole, itraconazole, clarithromycin or rifampicin.
- Have liver or kidney disease, head injury or raised pressure in the brain, low blood pressure, an underactive thyroid, or bowel obstruction.
- Are pregnant, planning pregnancy or breastfeeding.
- Are elderly or frail, where sensitivity is greater.
- Have a history of substance dependence.
Do not drive while starting treatment or after a dose change.
Ask your prescriber whether naloxone — the opioid reversal medicine — should be available at home, and make sure someone you live with knows the signs of overdose and how to call for help.
Possible cautions and when to ask a pharmacist or doctor
Common effects include drowsiness, nausea, vomiting, constipation, dry mouth, confusion, itching, sweating and skin irritation under the patch. Constipation is near-universal with opioids and does not improve with time — it should be managed with a laxative from the start, not once it becomes a problem.
Get emergency help immediately — call an ambulance — for:
- Slow, shallow or irregular breathing, or long pauses between breaths.
- Extreme drowsiness, or being difficult to wake.
- Blue or grey lips, fingertips or face.
- Pinpoint pupils with drowsiness.
- Limpness, or loss of consciousness.
These are signs of opioid overdose. If naloxone is available, give it and still call for help — it wears off before fentanyl does.
Also seek urgent advice for severe confusion or hallucinations, a seizure, chest pain, severe abdominal pain with no bowel movement, or swelling of the face and difficulty breathing.
Contact your doctor if pain is not controlled, if drowsiness is excessive, if a patch will not stay on, if you develop a fever, or if you want to stop. Do not stop suddenly after regular use — withdrawal is unpleasant and reduction should be planned. And if someone you care for seems unusually sleepy after a patch change, treat that as urgent rather than waiting to see.
Related medicine guides
Frequently asked questions
What is fentanyl used for? As an injection, for anaesthesia and severe acute pain in hospital. As a patch, for constant severe pain needing round-the-clock opioid treatment, most often in cancer and palliative care.
How strong is it? Roughly a hundred times more potent than morphine, which is why it is dosed in micrograms and classified Schedule 6.
Why does a patch take so long to work? It has to build up in the skin first, reaching full effect after 12 to 24 hours. Levels also fall slowly after removal, for the same reason.
Can I cut a patch to reduce the dose? No. Cutting can release the whole amount at once. Ask your doctor for a different strength.
Why does heat matter? Heat increases absorption through the skin. Hot baths, heat pads, saunas, direct sun and fever can all raise the dose delivered, sometimes dangerously.
What do I do with used patches? Fold them sticky sides together and return them to a pharmacy. Used patches still contain drug and have seriously harmed children and pets.
Is it addictive? Physical dependence develops with regular use, and it has a high potential for misuse. Used as prescribed for severe pain, with proper supervision, it has an established place.
What about fentanyl in street drugs? Illicitly made fentanyl is mixed into counterfeit tablets and other drugs and is a leading cause of overdose deaths. It cannot be detected by look or taste, and no precaution makes those products safe.