What is naltrexone?

Naltrexone hydrochloride is the active ingredient in naltrexone medicines. Naltrexone belongs to a group of medicines called opioid receptor antagonists.

In simple terms, it helps block the effects of opioids on specific receptors in the brain. Depending on the person’s needs, this can support treatment goals for opioid use disorder and for alcohol dependence by reducing rewarding effects and supporting abstinence-related strategies.

How naltrexone works (mechanism of action)

Naltrexone primarily acts as an antagonist at opioid receptors, especially:

• Mu (µ) opioid receptors
• Kappa (κ) and delta (δ) receptors to a lesser extent

By blocking these receptors, naltrexone reduces or prevents the effects of opioids such as morphine, oxycodone, heroin, codeine and other opioid medicines. This can make opioids less likely to produce the expected “rewarding” effects.

For alcohol dependence, naltrexone is thought to influence brain signalling involved in reward and reinforcement. While it does not treat withdrawal symptoms directly, it may help reduce heavy drinking and support abstinence strategies for some people.

Pharmacokinetics (how the body processes naltrexone)

Understanding pharmacokinetics can help explain why timing and adherence matter. Key features include metabolism, distribution, and how long effects may last.

Absorption

Naltrexone is absorbed after oral administration. Food may affect the speed of absorption, but generally does not remove the medicine’s overall effect.

Metabolism

Naltrexone is metabolised in the liver. A major metabolite is 6β-naltrexol. This metabolite also has opioid receptor antagonist activity, contributing to the overall effect.

Half-life and duration

The clinical duration of action depends on both naltrexone and its metabolites. On average, naltrexone’s activity and metabolite effects can extend beyond a single dosing interval, which is one reason dosing schedules are important.

Elimination

Naltrexone and its metabolites are eliminated mainly through the kidneys (urine). Dose selection may require additional caution in people with significant kidney problems.

Typical use and timing

Naltrexone is commonly used as part of a broader treatment plan that may include counselling and support. It is not the only component—behavioural and psychosocial support can improve outcomes.

When to start

Timing is especially important for opioid use disorder. Naltrexone blocks opioid receptors, so starting it too soon after opioid use can precipitate opioid withdrawal symptoms in some circumstances. For alcohol dependence, the approach may differ depending on your treatment plan.

How to take it (general timing principles)

• Take it at the same time each day to support routine.
• If you miss a dose, take it when you remember unless it’s close to the next dose—avoid doubling.
• If you’re switching from opioid-based medicines or using opioids for pain, discuss timing with a clinician.

Indications (what naltrexone is used for)

Naltrexone is used to assist with:

• Alcohol dependence (supporting reduction in heavy drinking and/or helping maintain abstinence for some people)
• Opioid dependence / opioid use disorder (helping prevent relapse by blocking opioid effects)

The suitability of naltrexone depends on your individual circumstances, including whether opioids are present in your system, liver health, and concurrent medications.

Dosing guidance (how much and how often)

Dosing can vary by indication, formulation, and individual factors such as liver function and tolerability. Always follow the dosing schedule provided for your product and your care plan.

Common oral dosing patterns

Many oral regimens use once-daily or time-limited approaches, depending on the condition. For safety and effectiveness, clinicians often use a careful start and monitoring plan.

If you need pain relief

Naltrexone can reduce the effects of opioid pain medicines. For acute pain, alternative pain management strategies may be needed (often non-opioid options). This should be discussed ahead of time where possible.

Missed dose

• If you miss a dose, take it as soon as you remember unless it’s close to the next scheduled dose.
• Do not take a double dose to make up for the missed tablet.
• If you’re unsure, seek guidance from a healthcare professional or pharmacist.

Food interactions (with meals and drinks)

Naltrexone is generally taken with or without food. Food may change how quickly it’s absorbed, but it usually does not significantly change the overall effect.

Practical tips:

• Choose a routine—e.g., morning or evening with a meal or snack—to help you remember.
• If you experience nausea or stomach upset, taking the dose with food may improve comfort.

Alcohol and medicine interactions

Alcohol while taking naltrexone

Naltrexone is used in alcohol dependence, so some people may still drink alcohol while starting therapy. However, drinking can interfere with treatment goals and may worsen risks.

• Alcohol may increase side effects such as dizziness, drowsiness, or nausea.
• If you drink heavily, it may increase the burden on the liver—important because naltrexone can also affect liver enzymes.
• For best outcomes, follow the drinking plan set by your healthcare team.

Opioids: the most important interaction

Naltrexone blocks opioid receptors. This means:

• Opioid medicines may not work as expected.
• Attempting to override blockade by taking opioids can be dangerous.
• If naltrexone is stopped, opioid sensitivity may change; overdose risk can increase if opioids are restarted without medical guidance.

Other medicines

Naltrexone may interact with certain medicines through metabolism or overlapping side effects. Tell your pharmacist or clinician about all medicines and supplements you use, including:

• Other drugs for substance use disorders
• Medications that affect the liver
• Medicines that cause drowsiness or dizziness (the combination may worsen these effects)

If you’re starting, stopping, or changing a medication, it’s a good idea to check for interactions. Your pharmacist can help identify relevant concerns.

Safety profile and warnings

Like all medicines, naltrexone can cause side effects. Most are mild to moderate, but some require prompt medical attention. Safety considerations also include liver health and the opioid-related risk of withdrawal if taken too soon.

Common side effects

• Nausea
• Headache
• Dizziness or light-headedness
• Fatigue or sleep disturbances
• Reduced appetite
• Stomach discomfort

Less common but important risks

• Liver enzyme changes: Naltrexone can affect liver function. Baseline and follow-up liver tests may be recommended.
• Opioid withdrawal symptoms: If opioids are still present in the body, starting naltrexone too soon can cause withdrawal.
• Allergic reactions: Seek immediate help if you develop swelling of the face/lips, trouble breathing, or widespread rash.

Who should be extra cautious

Extra caution may be needed if you have:

• Known liver disease or a history of elevated liver enzymes
• Any current or recent opioid use (including opioid medicines for pain)
• Significant kidney impairment (dose decisions may need adjustments)
• Other serious medical conditions or complex medication regimens

Driving and operating machinery

Some people experience dizziness or fatigue with naltrexone. Avoid driving or operating machinery until you know how the medicine affects you.

Overdose: what to do

Taking more than recommended can increase risk of significant side effects. If an overdose is suspected, seek urgent medical help or contact Poisons Information (Australia) for advice.

Emergency warning signs include severe vomiting, fainting, severe weakness, yellowing of the skin/eyes, or breathing difficulties. If these occur, seek emergency assistance immediately.

Practical use tips

The following tips can support safe, effective use and help reduce the chance of problems.

1) Review opioid exposure before starting

If you have used opioids recently—whether prescription, non-prescription, or accidental exposure—talk to your clinician. Timing matters to reduce the risk of withdrawal symptoms.

2) Plan for pain management

If you expect dental work, surgery, or ongoing pain treatment, make sure your care team knows you take naltrexone. This can help avoid ineffective opioid treatment and supports safer alternatives.

3) Monitor liver health if advised

Follow any blood test schedules recommended by your healthcare professional, especially if you have risk factors for liver problems.

4) Don’t stop abruptly without guidance

If you’re considering stopping due to side effects or changing your treatment plan, discuss this with a healthcare professional. Sudden changes can affect outcomes and safety, especially in substance use treatment contexts.

5) Use supportive routines

• Set a daily alarm or use a medication reminder app.
• Pair taking the tablet with a consistent daily activity (e.g., after breakfast).
• Consider counselling or support groups alongside medication.

Alternative options

Depending on your goals and clinical history, other options may be considered. Your clinician can help determine what’s most appropriate.

For opioid use disorder

• Buprenorphine (opioid partial agonist)
• Methadone (opioid full agonist)
• Psychosocial interventions and relapse-prevention programs

These alternatives differ in how they work and how they’re monitored. Some people may respond better to one approach than another.

For alcohol dependence

• Acamprosate (helps support abstinence-related goals in some people)
• Behavioural support and structured treatment programs
• Other clinician-recommended strategies

Choice of treatment depends on medical history, liver and kidney function, current substances, and personal preferences. Always discuss benefits and risks before switching.

Market and legal context for Australia

In Australia, medicines are regulated under the Therapeutic Goods Administration (TGA) framework and dispensed according to the Australian scheduling system. Availability may depend on the specific product brand, strength, and regulatory classification.

This online pharmacy page provides general patient information. Availability, prescribing requirements, and supply processes can vary based on product type and local pharmacy practices.

Important note: Naltrexone therapy should be coordinated as part of an appropriate healthcare plan, particularly if you have opioid exposure, liver disease, or are managing complex medication needs.

Recent guidance and monitoring (overview)

Clinical recommendations can evolve as new evidence and safety information become available. In general, current best practice for naltrexone use often includes:

• Assessment of opioid exposure prior to initiation (to reduce withdrawal risk)
• Liver function considerations (baseline and follow-up blood tests in appropriate patients)
• Medication review to identify opioid-containing medicines and potential interactions
• Ongoing support (counselling, relapse prevention planning, and monitoring of goals)

If you have liver disease, heavy alcohol use, or a history of opioid use, monitoring may be more frequent. Your pharmacist and clinician can advise what checks are suitable for your situation.

Delivery and availability

Availability depends on the specific naltrexone product you select (formulation and strength). For online orders in Australia, delivery options and timelines may vary by location and courier service.

What to expect when ordering online

• We aim to dispatch orders promptly after verification and processing.
• Delivery time estimates are typically provided at checkout.
• Orders may be split if stock is not immediately available.
• Cold-chain is generally not required for naltrexone tablets, but follow storage instructions on the pack.

Storage

• Store in a cool, dry place according to the product label.
• Keep out of reach of children.
• Check the expiry date before use.

If you have questions about whether a particular pack size or strength is suitable, contact our pharmacy team.

FAQ

1) Can I take naltrexone if I still use opioids?

Naltrexone blocks opioid receptors and may trigger withdrawal if opioids are still in your system. It’s important to discuss your opioid history and timing with your healthcare professional before starting.

2) Does naltrexone work immediately?

Some effects may be felt after the first dose, but treatment outcomes—especially for alcohol dependence—often depend on ongoing adherence and combined support over time.

3) Will naltrexone make opioid pain medicines useless?

Naltrexone can reduce or block the effects of opioid pain medicines while it’s active. If you require pain relief, ask your clinician or pharmacist about safe alternative options and timing.

4) What side effects are most common?

Common side effects include nausea, headache, dizziness, fatigue, and stomach discomfort. If side effects are severe or persistent, seek medical advice.

5) Are there food restrictions?

Naltrexone can usually be taken with or without food. If you experience nausea, taking it with food may help.

6) Can I drink alcohol while on naltrexone?

Naltrexone is used in alcohol dependence, but drinking alcohol can still undermine your treatment goals and may increase risks such as dizziness or liver strain. Follow the plan set by your healthcare team.

7) Does naltrexone affect the liver?

It can, in some people, raise liver enzymes or otherwise affect liver function. Your clinician may request blood tests, especially if you have risk factors.

8) What if I miss a dose?

Take it when you remember unless it’s close to the next dose. Do not take a double dose. If you’re unsure, consult your pharmacist.

9) Is it safe to drive?

If you feel dizzy or unusually tired, avoid driving or operating machinery until you know how naltrexone affects you.

10) What are the alternatives to naltrexone?

Alternatives may include medications such as acamprosate for alcohol dependence or medications like buprenorphine and methadone for opioid use disorder, alongside psychosocial support.

11) Where can I find product-specific details?

Always refer to the patient information leaflet included with your specific naltrexone product for complete details on side effects, storage, and dosing instructions.