Key Takeaways: Lariam Side Effects

Serious mental health risks: Lariam can cause depression, anxiety, hallucinations, and suicidal thoughts. Stop and seek help immediately if these occur.
Onset: Side effects can start within hours of the first dose or appear weeks later.
Duration: Most side effects resolve within weeks of stopping, but dizziness and mood changes can persist for months.
Contraindications: Do not take if you have depression, seizures, or certain heart problems.
Interactions: Avoid halofantrine and certain heart medications; check with your doctor.

Lariam (mefloquine) is effective at preventing malaria, but it can cause side effects ranging from mild to severe. Understanding when they start, how long they last, and who is at risk helps you use it safely. Always consult a doctor before starting.

Emergency Warning: When to Stop Lariam Immediately

Stop taking Lariam and seek medical help immediately if you experience: suicidal thoughts, self-endangering behaviour, severe anxiety, panic attacks, hallucinations, paranoia, confusion, or unusual aggression. These are medical emergencies.

When Do Lariam Side Effects Start?

Lariam side effects can begin at different times depending on the individual and the type of effect.

First dose (hours to days): Nausea, dizziness, headache, vivid dreams, and sleep disturbances often appear within the first few doses as your body adjusts.
During the first week: Insomnia, anxiety, and mild mood changes may develop.
Anytime during use (weeks to months): Serious neuropsychiatric effects like depression, psychosis, or hallucinations can occur at any point, even after several weeks of uneventful use.
After stopping: Some side effects (dizziness, vertigo, balance problems) can appear for the first time after you finish the course.

The long half-life of Lariam (2-3 weeks) means side effects can start or persist long after the last dose.

How Long Do Lariam Side Effects Last?

The duration of side effects varies widely. Here's what the evidence shows:

Side Effect Type	Typical Duration	Notes
Gastrointestinal (nausea, vomiting, diarrhoea)	Few hours to days	Often improve with continued use; taking with food helps
Sleep disturbances (insomnia, abnormal dreams)	1-4 weeks	May persist throughout treatment; often resolve after stopping
Dizziness, vertigo, loss of balance	Weeks to months	Can persist for months after stopping; report to your doctor
Neuropsychiatric (anxiety, depression, mood changes)	Weeks to months, sometimes longer	In a small number, depression may last a year or more; seek help
Serious mental health events (psychosis, hallucinations)	Variable; requires immediate treatment	Stop drug immediately; may need psychiatric care

Because Lariam has a half-life of 2-3 weeks, it takes about 10-15 weeks for the drug to be completely eliminated. Side effects can persist during this time.

Complete Side Effects Timeline

Here's a detailed breakdown of when specific side effects typically occur:

Very Common (affect more than 1 in 10 people)

Sleeping problems: Sleepiness, inability to sleep, bad dreams – usually within first week.

Common (affect up to 1 in 10 people)

Dizziness, headache, vision problems, loss of balance: Can start within hours of first dose and may persist.
Nausea, vomiting, diarrhoea, stomach ache: Often occur shortly after taking a dose; taking with food helps.
Itching: May appear at any time.
Depression, anxiety: Can develop gradually over weeks or appear suddenly.

Not known (frequency cannot be estimated)

Serious mental health: Suicide, attempted suicide, suicidal thoughts, self-endangering behaviour, psychosis, paranoia, panic attacks, aggression, confusion, hallucinations – can occur at any time, even after months of use.
Allergic reactions: Anaphylaxis, severe skin reactions (Stevens-Johnson syndrome) – usually within days to weeks.
Seizures: Can occur in people with or without a history of epilepsy.
Heart rhythm problems: Palpitations, slow heartbeat – may occur at any time.
Liver problems: Jaundice, dark urine – usually after prolonged use.
Neuropathy: Pins and needles, weakness, clumsiness – can develop slowly.
Vision and hearing changes: Cataract, blurred vision, tinnitus – variable onset.

After stopping: In a small number of patients, depression, dizziness, vertigo, and loss of balance may persist for months or longer.

Contraindications: Who Should NOT Take Lariam

Do not take Lariam if you have or have previously experienced:

Allergy: To mefloquine, quinine, quinidine, or any tablet ingredients.
Mental health conditions: Depression, suicidal thoughts, self-endangering behaviour, anxiety disorder, schizophrenia, psychosis, or any other mental problem.
Seizures: Epilepsy or any history of fits (convulsions).
Severe liver problems: Any significant liver disease.
Blackwater fever: A complication of malaria affecting blood and kidneys.
Concurrent use of halofantrine: Or use within the last 15 weeks – can cause dangerous heart rhythm changes.

Consult your doctor before use if you have:

Heart problems (especially rhythm disturbances like long QT).
Liver or kidney impairment.
Eye problems (loss of fine detail, colour vision changes).
Blood disorders (low white cells, red cells, or platelets).
Neuropathy (pins and needles, weakness).
Previous allergic reaction to Lariam.
Low blood glucose due to congenital hyperinsulinemic hypoglycaemia.

Food & Drug Interactions

Food Interactions

With food: Taking Lariam with a meal is recommended. Food may slightly delay absorption but reduces nausea and stomach upset.
Grapefruit: Grapefruit juice can inhibit CYP3A4 (the enzyme that metabolises Lariam) and potentially increase side effects. Avoid large amounts of grapefruit.
Alcohol: Moderate alcohol is not known to directly interact, but both can affect the liver and cause dizziness. Limit alcohol, especially if you experience neuropsychiatric symptoms.

Drug Interactions – Tell your doctor if you take:

Drug Class	Examples	Risk/Effect
Halofantrine	Halfan	Dangerous slowing of heart rate – absolutely contraindicated during and for 15 weeks after Lariam
Other antimalarials	Quinine, quinidine, chloroquine	Increased risk of seizures and heart rhythm problems
Heart medications	Beta-blockers, calcium channel blockers, antiarrhythmics	May affect heart rate and rhythm
Antihistamines	Cetirizine, loratadine, some older antihistamines	May increase risk of QT prolongation
Psychiatric medications	Tricyclic antidepressants (amitriptyline), SSRIs (fluoxetine), antipsychotics (phenothiazines)	Increased risk of seizures and heart effects
Anti-epileptics	Carbamazepine, phenytoin, phenobarbital, valproate	May reduce Lariam effectiveness; increased seizure risk
Antifungals	Ketoconazole	Avoid within 15 weeks after Lariam (increases Lariam levels)
Antibiotics	Rifampicin, some penicillins, cephalosporins	Rifampicin may reduce Lariam effectiveness
HIV medications	Efavirenz	Possible interaction; monitor
Painkillers	Tramadol	Increased risk of seizures
Blood thinners	Warfarin	May need monitoring
Diabetes medications	Insulin, oral hypoglycaemics	May need monitoring

Vaccines

If you need oral typhoid vaccine, take it at least 3 days before starting Lariam, as Lariam may stop the vaccine from working properly.

Lariam Side Effects FAQs

Can Lariam cause permanent side effects?

In rare cases, dizziness, balance problems, or depression have been reported to persist for months or years. Most side effects resolve after stopping, but some people may experience long-lasting symptoms.

What should I do if I experience anxiety or mood changes on Lariam?

Stop Lariam immediately and contact your doctor. These could be signs of serious neuropsychiatric side effects. Do not take another dose without medical advice.

Can I drink alcohol while taking Lariam?

Moderate alcohol is not strictly forbidden, but both can cause dizziness and affect the liver. If you experience any side effects, avoid alcohol completely.

Does Lariam interact with birth control pills?

There is no known direct interaction. However, if you experience vomiting or diarrhoea (possible side effects), contraceptive effectiveness may be reduced. Use additional protection.

Can I take Lariam if I have a family history of depression?

Lariam is generally not recommended for anyone with a personal or strong family history of depression or mental illness. Discuss alternatives with your doctor.

Need a Safer Alternative to Lariam?

If you're concerned about side effects, speak with a UK-registered doctor about other malaria prevention options like atovaquone-proguanil or doxycycline.