How Long Does Lariam Take to Work
Efficacy timelines for malaria prevention and treatment with Lariam (mefloquine).Learn more about malaria risks.
Key Takeaways
- Prevention: Full efficacy reached after 2 doses (10 days pre-travel)
- Treatment: Symptoms improve within 24-48 hours
- Duration: Weekly dosing maintains protection; continue 4 weeks post-travel
- Critical: No 100% guarantee—always use mosquito bite prevention
- Monitoring: Watch for delayed side effects (e.g., dizziness)
Understanding when Lariam starts working is crucial for effective malaria prevention and treatment planning.
Malaria Prevention Timeline
1st dose: Tests tolerance
2nd dose: Reaches therapeutic levels
Weekly doses maintain protection
Final dose covers incubation
Key Milestones
| Timeframe | Blood Concentration | Protection Level |
|---|---|---|
| After 1st dose | Low | Minimal (tests side effects only) |
| After 2nd dose | Therapeutic | ~90% against susceptible strains |
| Missed weekly dose | Sub-therapeutic | Protection drops significantly |
Note: Lariam does not protect against all malaria strains. Combine with mosquito bite prevention (DEET, nets).
Malaria Treatment Timeline
- 0-12 hours: Drug absorbed; begins attacking parasites
- 24-48 hours: Fever reduction, improved energy
- 3-7 days: Full symptom resolution (if susceptible strain)
Treatment vs. Prevention
| Treatment | Prevention | |
|---|---|---|
| Onset of Action | Within 24 hours | 10 days to reach efficacy |
| Dosing | Single high dose (may split) | Weekly low dose |
| Duration | One-time | Continue 4 weeks post-exposure |
Factors Affecting Efficacy
- Parasite resistance: Lariam is ineffective against some P. falciparum strains in Southeast Asia.
- Adherence: Missing weekly prevention doses drastically reduces protection.
- Food intake: Fatty meals improve absorption by 40%.
- Drug interactions: Halofantrine/quinine reduce efficacy and increase heart risks.
- Liver function: Impaired metabolism may delay therapeutic levels.
When to Seek Medical Help
- Fever persists >48 hours after treatment dose
- Neurological symptoms develop (confusion, seizures)
- Severe vomiting prevents dose retention
- Psychiatric side effects emerge (hallucinations, suicidal thoughts)
Post-Travel Monitoring
Malaria symptoms can appear up to 1 year after exposure. Report any fever to your doctor, even if you completed Lariam prophylaxis.
Frequently Asked Questions
Why does prevention require 10 days to work?
Lariam accumulates slowly in the blood. Two doses are needed to reach therapeutic levels and test for intolerable side effects.
Can I stop Lariam early if leaving the risk area?
No—complete all 4 post-travel doses. Malaria parasites can incubate for weeks after exposure.
How quickly does Lariam leave the body?
Half-life is 2-4 weeks. Side effects (e.g., dizziness) may persist for months after stopping.
Is Lariam effective against all malaria types?
No—it's primarily for P. falciparum. Resistance occurs in parts of Southeast Asia.
What if I miss a weekly prevention dose?
Take ASAP if ≤48 hours late. If >48 hours, skip and resume schedule. Use extra mosquito protection.
Need Treatment for malaria
If you're experiencing symptoms of a bacterial infection, our UK-registered doctors can help determine if Lariam Tablets is appropriate for your condition through a confidential online consultation.
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Medical Content Manager
Nabeel is a co-founder and medical content manager of Chemist Doctor. He works closely with our medical team to ensure the information is accurate and up-to-date.
Medical Doctor
Dr. Feroz is a GMC-registered doctor and a medical reviewer at Chemist Doctor. He oversees acute condition and urgent care guidance.
Medical Director
Usman is a co-founder and medical director of Chemist Doctor. He leads the organisation's strategic vision, bridging clinical and operational priorities.
Review Date: 03 November 2025
Next Review: 05 May 2026
Published on: 03 November 2025
Last Updated: 04 November 2025
