Key Takeaways: Lariam's Timeline

Onset: Lariam reaches peak blood levels 6–24 hours after a dose.
Half-life: Very long – 2 to 3 weeks (14–21 days).
Steady state: Achieved after 4–6 weeks of weekly dosing.
Protection: Continues for weeks after last dose – take for 4 weeks after return.
Efficacy: >90% effective when taken correctly, but no antimalarial is 100%.

Lariam (mefloquine) is a once-weekly antimalarial with a unique long half-life. Understanding its timeline helps you take it correctly and stay protected. Here's what happens from the moment you swallow the tablet.

Important Medical Advice

If you experience mood changes, anxiety, unusual thoughts, or dizziness while taking Lariam, stop and seek medical help immediately. These side effects can occur even weeks after stopping.

Onset of Action & Absorption Rate

Lariam is rapidly but variably absorbed after oral administration.

Absorption: Well absorbed from the gastrointestinal tract (bioavailability >85%).
Peak blood levels (Cmax): Achieved between 6 and 24 hours after a dose. The wide range is due to individual differences in metabolism and food intake.
Food effect: Taking Lariam with a meal can delay absorption slightly but reduces nausea and is recommended.

The onset of antimalarial action begins once blood levels are high enough to kill parasites, which is typically within the first day after a dose. However, for prevention, it's essential to have taken several doses to build up protective levels before exposure.

Efficacy Rate & Peak Concentration

Lariam's efficacy depends on maintaining adequate blood concentrations throughout the risk period.

Parameter	Value	Clinical Meaning
Peak concentration time	6–24 hours	Maximum drug levels reached within one day
Steady state	4–6 weeks of weekly dosing	Full protective levels after about a month
Efficacy rate (prevention)	>90% for sensitive strains	Very effective when taken consistently
Protein binding	~98%	Slow release from tissues contributes to long half-life

Note that efficacy can be lower in areas with mefloquine resistance (parts of Southeast Asia). Check current travel advice.

How Long Does Lariam Take to Enter the Body?

Lariam enters the bloodstream quickly after you swallow it.

0–6 hours: The tablet dissolves in the stomach and small intestine; the drug begins to be absorbed.
6–24 hours: Blood levels rise and reach their maximum. At this point, the drug is distributed throughout the body, including red blood cells where malaria parasites live.
24 hours onward: Levels slowly decline as the drug binds to tissues and is metabolised.

Because of the long half-life, a single dose provides a week's worth of protection. That's why it's taken weekly.

How Long Does Lariam Take to Leave the Body?

Lariam is eliminated very slowly, which is why it protects for weeks after the last dose.

Half-life: 14 to 21 days (average ~18 days). This means it takes that long for half the drug to be cleared.
Complete elimination: It takes about 5 half-lives (70–105 days, or 10–15 weeks) for Lariam to be almost completely gone from the body.
Metabolism: Lariam is broken down in the liver by the CYP3A4 enzyme into inactive metabolites, which are excreted mainly in bile and faeces. Only a small amount is excreted unchanged in urine.

This long elimination is why you continue taking it for 4 weeks after leaving a malaria area – to cover the parasite's incubation period. It also means side effects can persist or appear weeks after stopping.

Duration of Protection & Longevity

How long does one dose protect you? With a half-life of 2–3 weeks, a single dose maintains protective levels for about a week – hence the weekly schedule.

After your last dose, protective levels decline slowly:

1 week after last dose: Levels still high enough for protection (which is why you only need weekly dosing).
4 weeks after last dose: Levels have fallen but may still offer some protection – this is why you continue for 4 weeks post-travel.
3 months after last dose: Most of the drug has been eliminated, but trace amounts may remain.

To be fully protected, you must take the full course as prescribed: start 10 days before travel, continue weekly during travel, and finish 4 weeks after return.

Lariam Timeline FAQs

How soon after taking Lariam am I protected?

You need to have taken at least 2 doses (10 days and 3 days before travel) to build protective levels. Full protection is achieved after 4–6 weeks of weekly dosing.