Naltrexone blocks opioid receptors. It is used to treat alcohol dependence and opioid dependence, and at a much lower dose it appears in a weight-loss combination. It is not a sedative, it is not addictive, and taking it while opioids are in your system causes immediate, severe withdrawal.
What is Naltrexone?
The South African Medicine Price Registry lists naltrexone in two products:
| Product | Schedule | Contains |
|---|---|---|
| Naltima | S4 | Naltrexone hydrochloride 50 mg |
| Contrave | S5 | Naltrexone 8 mg + bupropion 90 mg |
Naltrexone is an opioid receptor antagonist. It binds to the same receptors as morphine, codeine, tramadol and heroin, but activates nothing — it simply occupies the site and blocks anything else from acting there.
Two consequences follow, and they explain both of its main uses.
Opioids stop working. Someone on naltrexone who takes heroin, morphine or codeine feels little or nothing, which removes the reward that drives use. This is the basis of its role in opioid dependence.
Alcohol becomes less rewarding. Drinking releases the body’s own endorphins, which act on the same receptors. Blocking them blunts the pleasure of drinking, reduces craving, and makes it easier to stop after one or two drinks rather than continuing. It does not make you sick if you drink — that is disulfiram, an entirely different medicine that people frequently confuse with this one.
The critical safety point. If opioids are still in your system, naltrexone displaces them from the receptors all at once and causes immediate, severe precipitated withdrawal — far worse and faster than natural withdrawal. You must be opioid-free before starting: usually 7 to 10 days off short-acting opioids and 10 to 14 days off methadone, confirmed by your prescriber. This is not a medicine to start on your own initiative.
A second safety point, equally important. Blocking the receptors reduces your tolerance to opioids. After stopping naltrexone — or if someone takes a large dose to override the block — the risk of fatal overdose is substantially increased. People have died attempting to overcome the blockade.
Contrave is a different proposition — 8 mg of naltrexone with bupropion, for weight management. The doses and purpose are quite separate from the 50 mg tablet.
What is Naltrexone commonly used for?
- Alcohol dependence — reducing craving, heavy drinking days, and relapse to heavy drinking. This is its commonest use, and the evidence is reasonably good.
- Opioid dependence, to prevent relapse after detoxification. It works only for someone who has already completed withdrawal and wants to stay off.
- Weight management, as the naltrexone-bupropion combination, alongside diet and exercise in people with obesity or overweight with related conditions.
- “Low-dose naltrexone” (LDN) — typically 1 to 5 mg — used off-label for fibromyalgia, chronic fatigue syndrome, Crohn’s disease and multiple sclerosis. The evidence is preliminary, it is not established treatment, and it requires compounding.
Three things determine whether it works.
It works best alongside psychological support. Naltrexone reduces craving; it does not address why someone drinks. Counselling, group programmes and structured support roughly double the benefit, and the medicine is not a substitute for them.
It is not the only option. For alcohol dependence, acamprosate and disulfiram are alternatives working differently, and for opioid dependence, methadone and buprenorphine are considerably more effective than naltrexone at keeping people in treatment and alive. Naltrexone suits a particular person: motivated, already withdrawn, and wanting no opioid at all.
Stopping drinking abruptly can be dangerous. In significant alcohol dependence, withdrawal can cause seizures and delirium tremens, which are life-threatening. Detoxification should be medically supervised — this is not something to attempt alone at home.
How Naltrexone fits into this medicine category
| Group | Examples | Role |
|---|---|---|
| Opioid antagonists | Naltrexone (Naltima), naloxone | Block opioid receptors |
| Opioid substitution | Methadone, buprenorphine | Replace the opioid; most effective for dependence |
| Alcohol dependence | Naltrexone, acamprosate, disulfiram | Craving, relapse prevention, deterrent |
| Weight management | Contrave, semaglutide, orlistat | Different mechanisms |
| Emergency reversal | Naloxone | Reverses opioid overdose |
Naloxone and naltrexone are easily confused. Naloxone is the short-acting injection or nasal spray that reverses an opioid overdose and saves lives in minutes. Naltrexone is the long-acting tablet used in ongoing treatment. If someone is overdosing, naloxone is what is needed — along with an ambulance.
See the general medicines hub, and other guides such as HP553 and K-Fenak OTC.
What to check before using Naltrexone
You must be opioid-free before starting. Your prescriber will confirm this, usually with a urine test and sometimes a naloxone challenge. Do not start it yourself.
Tell your doctor if you:
- Take any opioid, including codeine in painkillers or cough mixtures, tramadol, morphine, or methadone.
- Have liver disease or hepatitis. Liver function is checked before starting and periodically.
- Have kidney disease.
- Are pregnant, planning pregnancy or breastfeeding.
- Have depression or a history of self-harm.
- Are due for surgery, or have a condition likely to need strong pain relief.
Two things to arrange before you start:
Carry a card or wear a bracelet saying you take naltrexone. In an emergency, opioid painkillers will not work normally, and the team treating you needs to know. Tell any dentist, surgeon or emergency doctor.
Discuss pain relief in advance. Anti-inflammatories, paracetamol, local and regional anaesthesia all still work. For planned surgery, naltrexone is usually stopped 3 to 7 days beforehand.
Practical points:
- Take it once daily, at the same time, with or without food.
- Do not try to override the block. Taking large amounts of an opioid to feel an effect is how people die on this medicine.
- Do not stop and immediately use opioids. Your tolerance is reduced, and a previously normal dose can be fatal.
- Keep your liver blood tests.
- Engage with the psychological support offered. It is what makes the medicine work.
Possible cautions and when to ask a pharmacist or doctor
Common effects, mostly early and settling: nausea, headache, dizziness, tiredness, difficulty sleeping, anxiety, abdominal pain and joint or muscle aches.
Get emergency help for:
- Severe opioid withdrawal shortly after a dose — agitation, sweating, vomiting, diarrhoea, cramping, racing heart. This means opioids were still present.
- Yellowing of the skin or eyes, dark urine, pale stools, or severe upper abdominal pain — possible liver injury.
- Thoughts of harming yourself, or a marked worsening of mood. Contact a doctor, an emergency department, or the South African Depression and Anxiety Group.
- Suspected opioid overdose in anyone — naloxone and an ambulance, immediately.
- Swelling of the face, lips or tongue, or difficulty breathing.
Seek prompt advice for:
- Persistent nausea or vomiting.
- New or worsening low mood or anxiety.
- A rash.
- Needing pain relief for an injury or procedure.
- Wanting to stop the medicine — so the reduced opioid tolerance can be discussed first.
See a doctor if you relapse, or feel close to it. Relapse is common in dependence and is not a reason to stop treatment or to be ashamed — it is information about what needs adjusting. The people who do best are generally those who go back rather than disappear.
Related medicine guides
Frequently asked questions
What is naltrexone used for? Alcohol dependence and opioid dependence, by blocking opioid receptors. At a much lower dose, combined with bupropion, it is also used for weight management.
Does it make me sick if I drink? No — that is disulfiram, a different medicine. Naltrexone blunts the pleasure of drinking and reduces craving.
Is it addictive? No. It activates nothing and produces no high, craving or withdrawal of its own.
Why must I be opioid-free before starting? Because it displaces opioids from their receptors all at once, causing immediate severe withdrawal. Usually 7 to 10 days off short-acting opioids, and 10 to 14 days off methadone.
What if I need pain relief? Anti-inflammatories, paracetamol and local anaesthesia still work. Tell any dentist, surgeon or emergency doctor that you take it, and carry a card.
What happens if I take opioids anyway? They will do little or nothing, and taking large amounts to override the block is how people die on this medicine.
Is it dangerous to stop? Not in itself, but your opioid tolerance is reduced. A dose you once handled could be fatal after stopping.
What is low-dose naltrexone? An off-label use at 1 to 5 mg for conditions such as fibromyalgia and Crohn’s disease. The evidence is preliminary and it is not established treatment.
Is naltrexone the same as naloxone? No. Naloxone is the short-acting emergency treatment that reverses an opioid overdose. Naltrexone is the long-acting tablet used in ongoing treatment.