Can You Get Malaria Even After Taking Preventative Pills?

Yes, it is possible to get malaria even if you take your preventative pills (also called prophylaxis). While antimalarial medications are highly effective when used correctly, no drug provides 100% protection against the disease ^[1].

Patients are often confused and frustrated when they get sick despite taking their medication. However, standard preventative pills suppress the infection but may not completely prevent it in every scenario.

What to Do If You Have Malaria Symptoms Now

If you develop a fever, chills, or flu-like symptoms after traveling to a malaria-endemic area, seek urgent medical assessment—even if you took your pills perfectly, and even if it has been more than a year since you returned ^[2].

• Tell your care team: Inform them exactly where you traveled, what preventative pills you took, and your dosing schedule.
• A single test may not be enough: If your first blood smear or rapid test is negative, you still need close monitoring. A single negative test does not rule out malaria, especially if parasite levels are low or if you took prophylaxis ^[3]. Your doctor may need to repeat blood tests over 24 to 48 hours.
• Watch for severe signs: Seek immediate emergency care if you experience confusion, trouble breathing, repeated vomiting, severe weakness, fainting, or jaundice (yellowing of the eyes or skin).
• Prophylaxis is not treatment: The pills you took to prevent malaria are not adequate to treat an active infection.

Why Malaria Can Occur Despite Prophylaxis

When a person gets malaria despite taking preventative medication, it usually involves medication absorption, parasite biology, or drug resistance.

1. Adherence and Absorption Challenges

Preventative pills must be taken exactly as prescribed, but traveling makes this difficult. In 2018 U.S. surveillance, 95% of travelers who contracted malaria had either not taken or not fully adhered to a recommended regimen ^[1]. However, breakthrough infections can happen even with correct use. Common challenges include:

• Stopping too early: Depending on the medication, pills must be taken for a specific number of days or weeks after you leave the malaria zone. Stopping early leaves you unprotected against parasites emerging from your liver ^{[4] [1]}.
• Absorption issues: If you experience vomiting or severe diarrhea shortly after taking a dose, your body may not absorb it. (Always check your product instructions and contact a clinician or pharmacist promptly about whether a dose should be repeated. Some drugs, like atovaquone-proguanil, should be taken with food or a milky drink for proper absorption).
• Drug interactions: Certain other medications, including over-the-counter drugs, antacids, or specific HIV treatments, can interfere with how well your malaria pills work ^[5].

2. Dormant Liver Parasites

Malaria is caused by several species of parasites. Two specific types, Plasmodium vivax and Plasmodium ovale, can hide in your liver in a dormant (sleeping) state ^[6].

Most common travel antimalarials—including atovaquone-proguanil, doxycycline, and mefloquine—kill parasites in your blood but do not reliably clear these dormant liver forms ^{[6] [2]}. This means you may remain symptom-free during your trip, but weeks, months, or sometimes years after you stop taking the pills, the parasites can “wake up” and cause illness ^{[7] [6]}.

Note on Anti-Relapse Medication: To clear these dormant forms, doctors use medications like primaquine or tafenoquine. However, these drugs can cause serious blood complications (hemolytic anemia) in people with an enzyme deficiency called G6PD deficiency ^[2]. A clinician must order a G6PD blood test before prescribing these medications.

3. Drug Resistance

Malaria parasites are constantly evolving and have developed resistance to certain antimalarial medications ^[8]. For example, widespread resistance to the drug chloroquine in P. falciparum means it is no longer effective in many parts of the world, including most regions of Africa ^[9].

If you take a medication that the local parasites in your travel destination are resistant to, the pills will not protect you. This is why doctors must match your prescription to the specific, up-to-date resistance patterns of your exact destination ^[10].

The Importance of Layered Protection

Because no pill is 100% foolproof, travel medicine experts emphasize using multiple layers of protection ^[11]. Preventative medication must always be combined with strict bite prevention ^{[11] [12]}. To maximize your safety:

• Use effective repellents: Apply an EPA-registered insect repellent (like DEET) to exposed skin, following the label instructions to avoid the eyes, mouth, and broken skin ^{[13] [12]}.
• Sleep under a net: Use an insecticide-treated bed net, as many malaria-transmitting mosquitoes are highly active while you are in bed ^{[14] [15]}.
• Treat your clothing: Apply permethrin to your clothing and gear (never directly to your skin) for an extra barrier against bites ^[16].
• Stay aware during the day: While many malaria-carrying mosquitoes bite at night, some species also bite during the day, so bite prevention must be a 24-hour effort ^[17].