Lariam (Mefloquine)
Antimalarial Medication for Prevention and Treatment of Malaria
Quick Facts About Lariam
Key Takeaways About Lariam (Mefloquine)
- Weekly antimalarial prophylaxis: Lariam is taken once weekly, starting at least 1–3 weeks before travel and continuing for 4 weeks after leaving the malaria-endemic area
- Effective against resistant malaria: Mefloquine is active against Plasmodium falciparum strains that are resistant to chloroquine, which remains a significant global health concern
- Serious psychiatric warnings: Lariam can cause severe neuropsychiatric side effects including depression, anxiety, psychosis, hallucinations, and suicidal thoughts – stop immediately and seek medical help if these occur
- Contraindicated in psychiatric and seizure disorders: Do not take Lariam if you have a history of depression, anxiety, psychosis, schizophrenia, or epilepsy
- Long-lasting effects: Due to its very long half-life (2–4 weeks), some side effects may persist for months after stopping the medication
What Is Lariam and What Is It Used For?
Lariam (mefloquine) is an antimalarial medication that kills malaria parasites in the blood. It is used to prevent and treat malaria, a potentially life-threatening disease transmitted by infected mosquitoes in tropical and subtropical regions. Lariam is particularly valuable because it is effective against chloroquine-resistant strains of Plasmodium falciparum.
Malaria is caused by Plasmodium parasites that are transmitted to humans through the bites of infected female Anopheles mosquitoes. Once inside the human body, the parasites travel to the liver, where they mature and multiply. They then enter the bloodstream and invade red blood cells, where they continue to reproduce. As parasites burst out of red blood cells to infect new ones, they cause the characteristic cycles of fever, chills, and sweating associated with malaria. Without treatment, P. falciparum malaria can rapidly progress to severe complications including cerebral malaria, organ failure, and death.
Mefloquine, the active ingredient in Lariam, belongs to a class of drugs known as quinoline derivatives. It is structurally related to quinine, one of the oldest known antimalarial drugs. Mefloquine acts as a blood schizonticide, meaning it kills the asexual erythrocytic forms of the malaria parasite that are responsible for the clinical symptoms of the disease. Its mechanism of action is thought to involve the formation of toxic complexes with free haem within the parasitised red blood cells, which damages the parasite's cell membranes and leads to its death.
Lariam is effective against all four major species of Plasmodium that cause malaria in humans: P. falciparum, P. vivax, P. ovale, and P. malariae. Its most important clinical advantage is its activity against chloroquine-resistant P. falciparum, which is now widespread across much of sub-Saharan Africa, Southeast Asia, and South America. According to the World Health Organization (WHO), malaria caused an estimated 249 million cases and 608,000 deaths worldwide in 2022, with the vast majority occurring in Africa.
In malaria prophylaxis (prevention), Lariam is taken as a once-weekly tablet by travellers visiting malaria-endemic regions. The weekly dosing schedule is considered convenient compared to daily alternatives. Treatment should ideally begin at least three weeks before arrival in the endemic area to allow time for the drug to reach adequate blood levels and for any adverse effects to be identified before departure. It is continued throughout the stay and for four weeks after leaving the endemic area to kill any parasites that may still be in the blood from bites received during the final days of travel.
In malaria treatment, Lariam can be used to treat acute uncomplicated malaria. However, it is not recommended as first-line therapy for severe malaria, which requires intravenous artesunate or quinine. The treatment dose of mefloquine is significantly higher than the prophylactic dose and is typically split into two or three divided doses given six to eight hours apart to reduce the risk of gastrointestinal side effects.
Mefloquine was developed in the 1970s by the Walter Reed Army Institute of Research (WRAIR) as part of a programme to find new antimalarials effective against drug-resistant P. falciparum. It was approved for medical use in 1989 and remains on the WHO Model List of Essential Medicines. However, due to concerns about neuropsychiatric side effects, many travel medicine specialists now preferentially recommend alternative antimalarials such as atovaquone-proguanil (Malarone) or doxycycline, reserving mefloquine for situations where these alternatives are not suitable.
What Should You Know Before Taking Lariam?
Before starting Lariam, tell your doctor about any history of psychiatric illness, seizures, liver disease, or heart rhythm problems. Lariam is strictly contraindicated in people with depression, anxiety disorders, psychosis, epilepsy, or known hypersensitivity to mefloquine or related compounds such as quinine and chloroquine.
Mefloquine is a potent medication with a very long half-life, meaning it remains in the body for weeks after the last dose. This makes it essential that you are fully assessed by a doctor before starting treatment. A careful medical history is critical because certain pre-existing conditions greatly increase the risk of serious adverse effects. Your doctor will evaluate whether Lariam is the safest antimalarial option for you, or whether an alternative such as atovaquone-proguanil or doxycycline would be more appropriate.
Contraindications
You should not take Lariam if any of the following apply to you:
- Current or past history of depression, including suicidal thoughts or self-harm behaviour – mefloquine can trigger or worsen depressive episodes
- Any psychiatric disorder, including anxiety, schizophrenia, psychosis, bipolar disorder, or other mental health conditions
- Seizure disorders (epilepsy) or a history of convulsions – mefloquine lowers the seizure threshold
- Allergy to mefloquine or structurally related compounds such as quinine, quinidine, or chloroquine, or to any of the inactive ingredients in the tablet
- Severe liver problems – mefloquine is extensively metabolised by the liver
- Blackwater fever (haemoglobinuric fever) – a severe complication of malaria affecting the blood and kidneys
Lariam can cause serious psychiatric reactions in some patients. If you experience any of the following while taking Lariam, stop the medication immediately and seek medical attention: suicidal thoughts, self-harm urges, severe anxiety, paranoia, hallucinations (seeing or hearing things that are not there), nightmares, insomnia, depression, restlessness, confusion, or unusual behaviour. Your doctor should switch you to an alternative antimalarial immediately.
Warnings and Precautions
Talk to your doctor or pharmacist before taking Lariam if you have or have had any of the following conditions:
- Heart problems, particularly abnormal heart rhythms (arrhythmias) or conduction disorders – mefloquine can prolong the QTc interval and may interact with other drugs that affect heart rhythm
- Liver or kidney disease – impaired organ function can alter drug metabolism and increase the risk of adverse effects
- Lactose or galactose intolerance – Lariam tablets contain lactose monohydrate (50.6 mg per tablet) and should not be taken by people with congenital galactosaemia, glucose-galactose malabsorption, or Lapp lactase deficiency
- Eye problems – mefloquine may cause visual disturbances
- Blood disorders – including abnormal white blood cell counts, anaemia, or low platelet counts
- Neuropathy – symptoms such as numbness, tingling, weakness, or balance disturbances in the extremities
- Congenital hyperinsulinism – mefloquine may cause persistent low blood sugar in individuals with this condition
It is important to be aware that some adverse effects of Lariam can occur or persist after you stop taking the medication. In a small number of patients, depression, dizziness, vertigo, and balance disturbances have been reported to continue for months or longer after the last dose. This is attributed to the drug's exceptionally long half-life of two to four weeks.
Pregnancy and Breastfeeding
It is generally recommended that pregnant women avoid travelling to malaria-endemic areas, because malaria during pregnancy is associated with serious complications including miscarriage, premature delivery, low birth weight, and maternal death. If travel cannot be avoided, the choice of antimalarial prophylaxis must be carefully considered.
Lariam should ideally be avoided during pregnancy, particularly during the first trimester. However, the WHO states that mefloquine may be used in all trimesters of pregnancy when the benefits of malaria prevention outweigh the potential risks. Your doctor will make this decision based on your individual circumstances, including the level of malaria risk at your destination and the availability of alternative antimalarials.
Women of childbearing age should use effective contraception during treatment with Lariam and for at least three months after the last dose, due to the drug's very long elimination half-life.
Breastfeeding is not recommended while taking Lariam. Mefloquine passes into breast milk in small amounts. Although the quantity transferred is too small to protect a breastfed infant against malaria, the potential effects on the infant have not been fully established.
Driving and Operating Machinery
Lariam can cause dizziness, vertigo, balance disturbances, and psychiatric symptoms that may impair your ability to perform activities requiring alertness and fine motor coordination. You should exercise caution when driving vehicles, operating machinery, flying aircraft (pilots), or undertaking deep-water diving while taking this medication. In a small number of patients, these effects have been reported to persist for months or longer after stopping treatment. If you experience any neurological or psychiatric symptoms, you should refrain from these activities until the symptoms have fully resolved.
How Does Lariam Interact with Other Drugs?
Lariam interacts with several medications, most critically with halofantrin, which can cause life-threatening heart rhythm disturbances. Other significant interactions include antimalarials (quinine, chloroquine), anticonvulsants, beta-blockers, calcium channel blockers, and certain antifungals and antiretrovirals.
Because mefloquine has a very long elimination half-life of two to four weeks, drug interactions can persist for a considerable period after the last dose of Lariam. It is essential that you inform your doctor about all medications you are taking, including prescription drugs, over-the-counter medicines, and herbal supplements, before starting Lariam. Some interactions may require dose adjustments, monitoring, or the selection of an alternative antimalarial.
Major Interactions
| Drug | Category | Effect | Recommendation |
|---|---|---|---|
| Halofantrin | Antimalarial | Can cause serious, potentially fatal cardiac arrhythmias (significant QTc prolongation and slowed heart rate) | Do not take halofantrin during Lariam use or within 15 weeks of the last dose |
| Quinine / Quinidine | Antimalarial / Antiarrhythmic | Increased risk of seizures, cardiac arrhythmias, and QTc prolongation due to additive pharmacological effects | Use with extreme caution; allow adequate washout period between treatments |
| Chloroquine | Antimalarial | Increased risk of seizures when used together | Avoid concurrent use |
| Valproic acid (Valproate) | Anticonvulsant / Mood stabiliser | Mefloquine may reduce valproic acid levels, increasing seizure risk | Monitor valproic acid levels; consider alternative antimalarial |
| Carbamazepine / Phenytoin / Phenobarbital | Anticonvulsants | May reduce mefloquine blood levels; mefloquine may lower the seizure threshold | Avoid mefloquine in patients with epilepsy; use alternative antimalarial |
Other Notable Interactions
| Drug | Category | Effect | Recommendation |
|---|---|---|---|
| Beta-blockers | Blood pressure / Heart | Possible additive cardiac effects (bradycardia, conduction disturbances) | Use with caution; monitor heart rate and rhythm |
| Calcium channel blockers | Blood pressure / Heart | Possible additive cardiac effects | Use with caution; cardiac monitoring may be needed |
| Ketoconazole | Antifungal | May increase mefloquine blood levels | Consult your doctor; avoid ketoconazole within 15 weeks of last mefloquine dose |
| Rifampicin | Antibiotic (TB treatment) | May significantly reduce mefloquine blood levels, potentially reducing efficacy | Monitor for breakthrough malaria; consider alternative antimalarial |
| Efavirenz | Antiretroviral (HIV) | May reduce mefloquine blood levels | Monitor antimalarial efficacy; dose adjustment may be needed |
| Tricyclic antidepressants / Phenothiazines | Psychiatric medications | Increased risk of seizures and cardiac effects | Avoid combination; use alternative antimalarial |
| Antihistamines | Allergy medications | Possible additive cardiac effects with certain antihistamines | Use with caution; consult your doctor |
| Oral typhoid vaccine (Ty21a) | Live attenuated vaccine | Mefloquine may reduce the effectiveness of the oral typhoid vaccine | Complete typhoid vaccination at least 3 days before starting Lariam |
If you are taking anticoagulants (blood thinners) or medications for diabetes, your doctor may need to perform additional monitoring or follow-up tests before you travel. Mefloquine may alter the effects of these medications. Ensure you have a medical review well in advance of your departure date.
What Is the Correct Dosage of Lariam?
For malaria prevention, adults take one 250 mg Lariam tablet once weekly. Treatment should begin ideally 3 weeks (minimum 1 week) before entering a malaria area, continue throughout the stay, and for 4 weeks after leaving. For malaria treatment, the total dose is determined by body weight and is usually split into 2–3 doses given 6–8 hours apart.
Always take Lariam exactly as prescribed by your doctor. The dose and duration of treatment depend on whether you are taking the drug for malaria prevention (prophylaxis) or for the treatment of active malaria infection. Swallow the tablets with plenty of water, preferably with a meal or after eating, as food improves absorption and reduces gastrointestinal side effects. Do not chew the tablets as they taste extremely bitter. The scored tablets can be crushed and mixed with water if needed.
Adults – Prophylaxis (Prevention)
Standard Prophylactic Dose
1 tablet (250 mg) once weekly, taken on the same day each week.
- Start: Ideally 3 weeks before arrival in the malaria area (minimum 1 week)
- During travel: Continue weekly throughout the entire stay
- After travel: Continue for 4 weeks after leaving the malaria area
Starting 3 weeks before travel provides two important advantages: it allows the drug to reach protective blood levels, and it gives time to identify any intolerable side effects while a switch to an alternative antimalarial is still possible before departure.
Children
Paediatric Dosing
The dose for children is determined by the prescribing doctor based on body weight. Mefloquine is typically dosed at approximately 5 mg per kilogram of body weight once weekly for prophylaxis. The tablet can be divided using the score lines, allowing quarter-tablet doses. The same timing rules apply as for adults: start at least 1 week before travel, continue throughout the stay, and for 4 weeks after leaving the malaria area.
Adults – Treatment of Malaria
Therapeutic Dose
The treatment dose is determined by your doctor and is based on body weight. The total dose is typically 20–25 mg per kilogram of body weight. To reduce the risk of gastrointestinal side effects, the total dose is usually divided into 2 or 3 smaller doses given 6–8 hours apart. For partially immune individuals (people living in malaria-endemic regions), the standard treatment dose is used.
Missed Dose
If you miss a weekly prophylactic dose, take it as soon as you remember, then return to your regular weekly schedule. If it is nearly time for your next dose, skip the missed dose and take the next one as planned. Do not take a double dose to make up for a missed one.
Overdose
Taking more Lariam than prescribed increases the risk and severity of side effects, particularly neuropsychiatric and cardiac adverse effects. There is no specific antidote for mefloquine overdose. If you suspect an overdose, seek emergency medical attention immediately. Treatment is supportive and symptomatic, with particular attention to cardiac monitoring and management of seizures or psychiatric disturbances.
If you vomit within 30 minutes of taking a dose, take an additional full dose. If vomiting occurs between 30 and 60 minutes after the dose, take an additional half dose. If vomiting continues, contact your doctor for advice on alternative arrangements.
What Are the Side Effects of Lariam?
The most common side effects of Lariam are abnormal dreams, nightmares, and insomnia, occurring in more than 1 in 10 users. Depression and anxiety are common (up to 1 in 10). The most serious concerns are neuropsychiatric reactions including hallucinations, psychosis, suicidal behaviour, and seizures. Side effects are more frequent when Lariam is used for treatment (higher dose) than for prophylaxis.
Like all medicines, Lariam can cause side effects, although not everybody gets them. Adverse effects occur more frequently when mefloquine is used at the higher doses required for the treatment of acute malaria than when it is given at the lower prophylactic dose. It is critically important to recognise the early signs of serious side effects, particularly psychiatric symptoms, and to act on them promptly. If you develop any concerning symptoms during Lariam treatment, you should stop taking the medication and contact your healthcare provider immediately.
Neuropsychiatric Side Effects
Mefloquine is well known for its potential to cause neuropsychiatric adverse effects. These are the primary reason why many travel medicine practitioners now preferentially recommend alternative antimalarials. The psychiatric side effects can range from mild (vivid dreams, difficulty sleeping) to severe and potentially life-threatening (psychosis, suicidal behaviour). The following grid categorises the neuropsychiatric effects by their reported frequency:
Very Common
Affects more than 1 in 10 people
- Abnormal dreams and nightmares
- Difficulty falling or staying asleep (insomnia)
Common
Affects up to 1 in 10 people
- Depression
- Severe anxiety
Reported (Frequency Unknown)
Reported in post-marketing surveillance
- Suicidal thoughts, suicide attempts, and completed suicide
- Self-harm behaviour
- Psychosis (including delusions, personality changes, mania, and schizophrenia-like symptoms)
- Paranoia (feelings of mistrust towards others)
- Hallucinations (seeing or hearing things that are not there)
- Panic attacks
- Confusion and disorientation
- Aggression and agitation
- Restlessness
- Mood changes and emotional instability
- Bipolar disorder
- Concentration difficulties
- Abnormal behaviour
Other Side Effects
Common
Affects up to 1 in 10 people
- Dizziness and headache
- Visual disturbances
- Balance problems (vertigo)
- Nausea and vomiting
- Diarrhoea
- Abdominal pain
- Itching (pruritus)
Reported (Frequency Unknown)
Reported in post-marketing surveillance
- Anaphylaxis (severe allergic reaction) with breathing difficulties, swollen tongue, itching, and severe skin rashes
- Seizures (convulsions)
- Cardiac arrhythmias including palpitations, rapid or irregular heartbeat
- Stevens-Johnson syndrome and erythema multiforme (severe skin reactions with blistering)
- Pneumonitis (allergic inflammation of the lungs causing fever, cough, and breathing difficulties)
- Severe liver problems (tender or enlarged liver, jaundice, dark urine, pale stools)
- Agranulocytosis (severe reduction in white blood cells, weakening immune defence)
- Changes in blood pressure or heart rhythm disturbances
- Memory loss and forgetfulness (sometimes long-lasting)
- Speech difficulties
- Neuropathy (numbness, tingling, weakness in extremities)
- Drowsiness and fainting
- Tinnitus (ringing in the ears) and hearing loss
- Light sensitivity and blurred vision
- Shortness of breath and cough
- Impaired kidney function
- Decreased appetite
- Hair loss
- Excessive sweating
- Muscle weakness, cramps, and pain
- Joint pain
- Skin swelling (oedema)
- Chest pain, fatigue, and fever or chills
Some adverse effects can continue after you stop taking Lariam. In a small number of patients, depression, dizziness, vertigo, and balance disturbances have been reported to persist for months or even longer after the last dose. This is likely related to the drug's very long half-life (2–4 weeks). If you experience persistent neuropsychiatric or neurological symptoms after stopping Lariam, consult your doctor.
How Should You Store Lariam?
Store Lariam in its original packaging, protected from moisture, at room temperature. Keep out of sight and reach of children. Do not use after the expiry date printed on the carton.
Lariam tablets should be stored in their original blister packaging to protect them from moisture, which can degrade the medication. Store at room temperature (below 30°C / 86°F) and away from direct sunlight and heat. When travelling to tropical regions, take care to keep the tablets in a cool, dry environment – avoid leaving them in a hot car or in direct sun.
Keep this medicine out of the sight and reach of children. Do not use Lariam after the expiry date shown on the packaging. The expiry date refers to the last day of that month.
Do not dispose of medicines by flushing them down the toilet or placing them in household waste. Ask your pharmacist how to dispose of medicines you no longer use. These measures help to protect the environment.
What Does Lariam Contain?
Each Lariam tablet contains 250 mg of mefloquine (as mefloquine hydrochloride). The tablets are round, white to off-white, scored on both sides, and supplied in blister packs of 8 tablets.
Active Ingredient
The active substance is mefloquine 250 mg per tablet (as mefloquine hydrochloride).
Inactive Ingredients (Excipients)
The other ingredients are: lactose monohydrate (50.6 mg), poloxamer, microcrystalline cellulose, maize starch, crospovidone, ammonium calcium alginate, talc, and magnesium stearate.
Tablet Description
Lariam tablets are round, flat, white to off-white, with bevelled edges, measuring 12.1 mm in diameter and 3.7 mm thick. They are embossed with "LA-RI-AM-CP" on one side and have score lines on both sides. The tablet can be divided into four equal quarter-doses.
Packaging
Lariam is supplied in blister packs containing 8 tablets. The marketing authorisation holder is CHEPLAPHARM Arzneimittel GmbH, Greifswald, Germany.
Frequently Asked Questions About Lariam
Lariam (mefloquine) is an antimalarial medication used for the prevention (prophylaxis) and treatment of malaria. It is particularly effective against Plasmodium falciparum malaria, including chloroquine-resistant strains. For prevention, it is taken as a once-weekly tablet starting before travel to malaria-endemic areas, continued during the stay, and for four weeks after leaving. It is also used to treat acute uncomplicated malaria at higher doses under medical supervision.
The most serious side effects of Lariam are neuropsychiatric reactions. These include depression, severe anxiety, psychosis, hallucinations, paranoia, suicidal thoughts, and seizures. These effects can occur during use or after stopping the medication and may persist for months or longer. If you experience any psychiatric symptoms while taking Lariam, you should stop the medication immediately and seek urgent medical attention. Your doctor will switch you to an alternative antimalarial.
You should ideally start taking Lariam at least 3 weeks (21 days) before arriving in a malaria-endemic area, though the minimum recommended lead time is 1 week. Starting 3 weeks early has two advantages: first, it allows adequate drug levels to build up in your blood for full protection; second, it provides a trial period of 2–3 doses to check whether you tolerate the medication, giving you time to switch to an alternative if side effects develop. Continue taking it weekly throughout your stay and for 4 weeks after leaving the area.
No. Lariam (mefloquine) is strictly contraindicated in people with a current or past history of depression, anxiety disorders, psychosis, schizophrenia, bipolar disorder, or other psychiatric conditions. Mefloquine can trigger or significantly worsen these conditions, potentially leading to serious consequences including suicidal behaviour. If you have any history of mental health problems, discuss alternative antimalarial options with your doctor, such as atovaquone-proguanil (Malarone), doxycycline, or tafenoquine.
Lariam should generally be avoided during pregnancy, especially in the first trimester, due to limited safety data. However, the WHO states that mefloquine may be used in all trimesters when the benefits of malaria prevention clearly outweigh the risks. Pregnant women are strongly advised to avoid travel to malaria-endemic regions altogether. If travel is unavoidable, your doctor will make a risk-benefit assessment and may prescribe Lariam or an alternative antimalarial. Women of childbearing age should use effective contraception during treatment and for at least 3 months after the last dose.
Most side effects of Lariam resolve within days to a few weeks of stopping the medication. However, mefloquine has an unusually long half-life of 2 to 4 weeks, meaning the drug remains in the body for a considerable time after the last dose. In a small number of patients, neuropsychiatric side effects such as depression, dizziness, vertigo, and balance disturbances have been reported to persist for several months or even longer after discontinuation. If you experience persistent side effects, consult your healthcare provider for evaluation and management.
References
- World Health Organization (WHO). WHO Guidelines for Malaria. Geneva: WHO; 2023. Available from: who.int/publications/i/item/guidelines-for-malaria
- World Health Organization (WHO). World Malaria Report 2023. Geneva: WHO; 2023. Available from: who.int/teams/global-malaria-programme/reports/world-malaria-report-2023
- Centers for Disease Control and Prevention (CDC). CDC Yellow Book 2024: Health Information for International Travel. Chapter 5: Malaria. Available from: wwwnc.cdc.gov/travel/yellowbook
- European Medicines Agency (EMA). Lariam (mefloquine) – Summary of Product Characteristics. Available from: ema.europa.eu
- U.S. Food and Drug Administration (FDA). Mefloquine hydrochloride – prescribing information. Updated 2023. Available from: accessdata.fda.gov
- Schlagenhauf P, Adamcova M, Regep L, Schaerer MT, Rhein HG. The position of mefloquine as a 21st century malaria chemoprophylaxis. Malar J. 2010;9:357. doi:10.1186/1475-2875-9-357
- Ritchie EC, Block J, Nevin RL. Psychiatric side effects of mefloquine: applications to forensic psychiatry. J Am Acad Psychiatry Law. 2013;41(2):224-235.
- Tickell-Painter M, Maayan N, Saunders R, Pace C, Sinclair D. Mefloquine for preventing malaria during travel to endemic areas. Cochrane Database Syst Rev. 2017;10(10):CD006491. doi:10.1002/14651858.CD006491.pub4
- British National Formulary (BNF). Mefloquine. Available from: bnf.nice.org.uk/drugs/mefloquine
- WHO Model List of Essential Medicines – 23rd List (2023). Geneva: World Health Organization; 2023.
Editorial Team
This article was prepared and reviewed by the iMedic Medical Editorial Team, comprising licensed physicians with specialisations in infectious diseases, travel medicine, and clinical pharmacology. All content is reviewed according to international medical guidelines (WHO, CDC, ECDC, BNF) and follows the GRADE evidence framework.
iMedic Medical Editors – specialists in infectious diseases and clinical pharmacology with expertise in antimalarial therapy and travel medicine.
iMedic Medical Review Board – independent panel of medical experts ensuring accuracy, completeness, and adherence to current evidence-based guidelines.
Conflict of interest: The iMedic editorial team operates independently of pharmaceutical companies. This article is not sponsored by or affiliated with the manufacturer of Lariam. No commercial funding was received for this content.