A weekly antimalarial (Lariam)
Mefloquine
A once-weekly antimalarial tablet for preventing malaria, with important mental and mood side effects.
What is Mefloquine?
Mefloquine (Lariam) is an antimalarial tablet taken just once a week to prevent malaria in travellers, which makes it convenient for longer trips. However, it is well known for effects on mood and the mind, such as anxiety, vivid or disturbing dreams, low mood and, rarely, more serious mental health problems. Because of this it is avoided in people with a history of depression, anxiety, other psychiatric conditions or epilepsy. It is usually started a couple of weeks before travel so any reaction shows up early, and as with all antimalarials, bite-avoidance still matters and fever after travel needs urgent checking.
Education and reference only. This is a plain-language guide to Mefloquine — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Mefloquine, sold as Lariam, is an antimalarial medicine taken by mouth to prevent malaria in people travelling to areas where it is found. Its main practical feature is that it is taken only once a week, which suits longer trips. It is best known for its potential effects on mood and mental health, which mean it is not suitable for everyone and is chosen carefully. As well as preventing malaria, it is sometimes used (at a higher treatment dose, under medical supervision) to treat malaria. It is taken as a tablet with food and plenty of water.
How it works
Mefloquine kills the malaria parasite at the stage where it lives inside red blood cells, stopping an infection from taking hold after a mosquito bite. Because it stays in the body for a long time, a single weekly dose is enough to keep protective levels present. This long stay in the body is also why it is usually started a couple of weeks before travel, so that any side effects, particularly on mood or sleep, become apparent before the trip and an alternative can be chosen if needed.
Company & origin
Originated / developed by: Generic (long-established).
A once-weekly antimalarial used in the UK to prevent malaria, known for important effects on mood and the mind.
Practical use
How to take Mefloquine
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it once a week on the same day each week, with food and a full glass of water.
- Start it a couple of weeks before travel as advised, so any side effects on mood or sleep show up early.
- Continue the weekly dose throughout your trip and for the period after returning that you were told.
- Stop it and seek advice promptly if you develop anxiety, low mood, restlessness, confusion or disturbing dreams.
- Keep using mosquito-bite protection such as repellent, covering up and a net, because no tablet is fully protective.
- Seek urgent medical help for any fever or flu-like illness during or after travel, mentioning where you have been.
Weighing it up
Advantages & disadvantages of Mefloquine
Advantages
- Only needs to be taken once a week, which is convenient for longer trips.
- Effective for preventing malaria, including some areas where other tablets are less suitable.
- Can be used in pregnancy in some situations when advised by a specialist.
Disadvantages
- Can cause anxiety, low mood, vivid dreams and, rarely, serious mental health effects.
- Must be started well before travel so reactions can be spotted early.
- Not suitable for people with a history of depression, anxiety, other psychiatric illness or epilepsy.
Practical use
Good to know
The convenience of once-a-week dosing has to be weighed against mefloquine's well-known effects on the mind: anxiety, vivid or frightening dreams, sleep problems, dizziness, low mood and, rarely, more serious reactions such as hallucinations or psychosis. Because of this it is avoided in people with a history of depression, anxiety, other psychiatric illness, or seizures. It is usually started a couple of weeks before travel so any reaction shows up while alternatives are still possible, and it should be stopped and reviewed if disturbing mood or neurological symptoms appear. It is also generally avoided in people doing tasks needing fine balance or coordination, such as divers and aircrew. As with every antimalarial, repellent, covering up and a net still matter, and fever after travel must be checked urgently.
Who should not take it / use with caution
- People with a history of depression, anxiety, psychosis or other psychiatric conditions should not take it.
- People with epilepsy or a history of seizures, as it can lower the seizure threshold.
- Those with certain heart-rhythm conditions, or doing tasks needing fine balance such as diving or flying, should avoid it.
Monitoring
- Reviewing mental health history carefully before prescribing, and choosing an alternative if needed.
- Watching for mood, sleep or neurological changes, especially in the first few weeks.
- Watching for any fever after travel, which must be investigated urgently for malaria.
Side effects
- Vivid or disturbing dreams, sleep problems, anxiety, low mood and dizziness are well recognised.
- Headache, nausea, stomach upset or diarrhoea in some people.
- Rarely, more serious reactions such as confusion, hallucinations, psychosis or seizures, which need urgent help.
Key interactions
- It can add to the effects of medicines that affect heart rhythm, so these combinations are used cautiously.
- Other antimalarials such as quinine can increase the risk of heart-rhythm and neurological effects.
- Some anti-epileptic medicines can be affected, and their seizure control may be reduced.
Available as: Tablets taken by mouth once a week.
Answers
Mefloquine: frequently asked questions
Why is mefloquine only taken once a week?
It stays in the body for a long time, so a single weekly dose keeps enough in the system to protect against malaria; this makes it convenient for longer trips.
Is it true it can affect your mood?
Yes. Mefloquine is well known for effects such as anxiety, vivid dreams, low mood and, rarely, more serious mental health reactions, which is why it is chosen carefully and avoided in some people.
Who should not take mefloquine?
It is avoided in people with a history of depression, anxiety, other psychiatric conditions or epilepsy, and in some with heart-rhythm problems or jobs needing fine balance.
Why start it before I travel?
Starting a couple of weeks before travel lets any side effects on mood or sleep show up early, so an alternative can be arranged before your trip if needed.
What should I do if I get a fever after my trip?
Treat any fever during or after travel as possible malaria and seek urgent medical help, mentioning where you have been, even if you took your tablets.
The wider class
About Antimalarials
Mefloquine belongs to the antimalarials class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
Browse by body system
Authoritative sources
- BNF
- NICE CKS
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