Mefloquine Side Effects: What to Expect and When to Call Your Doctor

Mefloquine is an effective antimalarial, but it carries one of the most serious warning labels in travel medicine. In July 2013, the FDA added a boxed warning — its strongest warning type — to mefloquine's label, describing neurological and psychiatric side effects that can occur during or after treatment and may be permanent. Understanding these risks is essential before you start taking it.

This guide covers what side effects are common and manageable, which are serious and require immediate medical attention, and what the FDA's black box warning means for you as a patient.

Common Side Effects of Mefloquine

Most people who take mefloquine tolerate it without serious problems. The most common side effects are gastrointestinal and neurological, and many resolve as your body adjusts:

Nausea and vomiting

Diarrhea and stomach pain

Headache

Dizziness (mild)

Difficulty sleeping and vivid dreams or nightmares

Skin rash

To reduce GI side effects, always take mefloquine with food — ideally your largest meal of the day — and with at least 8 oz (240 mL) of water. Taking it with a meal also improves absorption.

Serious Side Effects: The Black Box Warning

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Neurological Side Effects (Stop Taking and Call Your Doctor)

Severe dizziness or vertigo (feeling that you or the room is spinning)

Loss of balance or coordination problems

Tinnitus (ringing in the ears)

Seizures or convulsions

Vision changes or eye damage

Psychiatric Side Effects (Stop Taking and Seek Medical Help)

Anxiety, paranoia, or feelings of mistrust

Depression or low mood

Hallucinations (seeing or hearing things that aren't there)

Psychotic behavior or delusional thinking

Suicidal thoughts or actions — call 911 or text/call 988 (Suicide & Crisis Lifeline) immediately

Confusion or unusual behavior

Critical point: These psychiatric symptoms can continue for months or even years after you stop taking mefloquine. If you experience any psychiatric symptoms after stopping mefloquine, tell your doctor and mention you took this medication — even if it was years ago.

Other Serious Side Effects

Liver damage (hepatotoxicity): Signs include nausea, yellowing of skin or eyes (jaundice), dark urine, upper right abdominal pain. Call your doctor promptly.

Cardiac effects: ECG changes including QTc interval alterations (risk is increased when combined with halofantrine, ketoconazole, quinine, or quinidine). Tell your doctor about all medications before starting mefloquine.

Allergic reactions: Hives, difficulty breathing, swelling of face/throat — seek emergency care immediately.

Who Should NOT Take Mefloquine?

Mefloquine should NOT be taken for malaria prevention if you have:

Active depression or a recent history of depression

Generalized anxiety disorder, psychosis, or schizophrenia

A history of seizures or convulsions

Allergy to mefloquine, quinine, or quinidine

Smart Monitoring Tips While Taking Mefloquine

Start mefloquine 2-3 weeks before departure (not the night before your trip) so you can monitor for side effects while still at home.

Tell a travel companion or family member that you're taking mefloquine and ask them to monitor your behavior — some psychiatric symptoms are more obvious to others than to the person experiencing them.

Do not drive or operate heavy machinery until you know how mefloquine affects you — dizziness and coordination problems can impair your ability to do so safely.

Carry the medfinder wallet card that comes with your prescription — it contains important safety information to share with healthcare providers in an emergency.

For information on drug interactions that can make mefloquine more dangerous, see: Mefloquine Drug Interactions: What to Avoid. If you need help finding mefloquine in stock, medfinder can locate it at pharmacies near you.