Chloroquine: Uses, Dosage, Side Effects, and Safety in 2025

People search this drug when they’re planning a trip, staring at an old prescription, or trying to separate hype from facts. Here’s the short, no-spin version: chloroquine still treats and prevents malaria-but only in a handful of places-while carrying real safety risks if used wrong. It is not a COVID fix. If you want to know when to use it, when to avoid it, and what to pick instead, you’re in the right spot.

TL;DR

• Purpose: An older antimalarial for treatment and weekly prophylaxis in areas where malaria remains sensitive to it; also used as adjunct therapy for certain amebiasis cases.
• Not for COVID-19: Large randomized trials (RECOVERY; WHO Solidarity) showed no benefit; major guidelines advise against it.
• Safety: Can prolong QT, trigger severe overdose toxicity, and cause retinal damage with long-term use; many drug interactions. Keep out of children’s reach.
• Dosing basics: For travel prevention, it’s a weekly regimen; for treatment, dosing is weight-based over 3 days (per CDC/WHO). Base vs salt labeling matters.
• Alternatives: In most destinations, resistance means you’ll use atovaquone-proguanil, doxycycline, mefloquine, or tafenoquine instead.

What chloroquine is-and where it actually fits in 2025

Chloroquine is a 4-aminoquinoline antimalarial that’s been around since the 1940s. It concentrates in the parasite’s food vacuole and disrupts heme detoxification, killing blood-stage Plasmodium. That makes it effective against the blood phase of malaria when the parasite is still circulating-before it overwhelms organs.

Approved roles in 2025

• Malaria treatment: Only where local Plasmodium falciparum remains susceptible. In many countries, resistance makes chloroquine a poor choice. It can still be used for P. vivax in some spots, but remember: chloroquine doesn’t clear dormant liver hypnozoites (so P. vivax/ovale relapses still happen unless treated with primaquine or tafenoquine after G6PD testing).
• Malaria prophylaxis: Weekly dosing for travelers headed to regions where resistance is rare. This is now a minority of global destinations.
• Extraintestinal amebiasis: Sometimes used as adjunct therapy (for liver involvement), not as first-line and not for intestinal disease.

What it’s not

• Not a COVID-19 treatment or preventive. The UK’s RECOVERY trial and WHO’s Solidarity trial found no mortality or clinical benefit. U.S. NIH, WHO, and most national guidelines recommend against it (and hydroxychloroquine) for COVID-19 outside clinical trials.
• Not interchangeable with hydroxychloroquine for autoimmune diseases. Hydroxychloroquine is preferred for lupus and rheumatoid arthritis because it’s better tolerated and safer for long-term use.

Why it fell out of favor (but didn’t disappear)

Drug resistance reshaped malaria care. From Africa to parts of Asia and Oceania, P. falciparum developed robust chloroquine resistance, so travelers and clinicians pivoted to other drugs. Pockets of sensitivity persist, though, so chloroquine still matters-just in narrower lanes. The U.S. CDC’s country tables (Yellow Book 2024-2025) and WHO malaria guidelines (2023 updates) remain the go-to maps for whether chloroquine is appropriate for a specific trip or case.

How it works in real life

• Fast action on blood stages: Good for suppressing acute symptoms in sensitive infections.
• No effect on liver dormancy: Radical cure for P. vivax/ovale needs primaquine or tafenoquine, both of which require a normal quantitative G6PD test before use.
• Weekly prevention is convenient: Once-a-week prophylaxis helps adherence, which is a plus for long trips-if your destination is chloroquine-sensitive.

Evidence corner (no links, just what to look up): RECOVERY trial (NEJM, 2020) and WHO Solidarity (2021) for COVID-19 ineffectiveness; WHO Guidelines for Malaria (2023) for where chloroquine still applies; CDC Yellow Book 2024-2025 for traveler dosing and maps; FDA label (chloroquine phosphate) revised 2024 for safety details.

Safe use: dosing basics, side effects, interactions, and who should avoid it

Before anything else, talk to a clinician who knows your destination and your health history. Self-medicating with antimalarials is a risky idea, and aquarium-grade products are not pharmaceutical-grade-people have been harmed by them.

Dosing 101 (big-picture, not a prescription)

• Label confusion: Chloroquine phosphate tablets are labeled by salt, but dosing is based on chloroquine base. One common tablet strength is 500 mg phosphate (about 300 mg base). Always verify base vs salt on the package.
• Prophylaxis: Weekly dosing, started 1-2 weeks before travel, taken once weekly during travel, and continued for 4 weeks after leaving the area. Typical adult regimen uses the equivalent of 300 mg base weekly (often 500 mg salt), but clinicians may adjust for weight and tolerance.
• Treatment: Weight-based over 3 days, commonly totaling 25 mg base/kg (10 mg base/kg initially, 10 mg base/kg at 24 hours, 5 mg base/kg at 48 hours) per CDC/WHO guidance-only for chloroquine-sensitive malaria. Do not improvise dosing; mis-dosing can be dangerous.
• Kids: Strictly weight-based. Because overdose can be rapidly fatal in children, keep the bottle locked away. Even a few tablets can be catastrophic for a toddler.

Common side effects

• GI upset: Nausea, stomach pain, vomiting. Taking with food helps.
• Headache and dizziness: Usually mild, but can affect balance-avoid risky activities until you know how you feel.
• Itchy skin (pruritus): Especially reported by people with darker skin tones. Often manageable but annoying.

Less common but important

• Hypoglycemia: Can lower blood sugar, sometimes severely. Diabetics should monitor closely; know the signs (sweating, confusion, shakiness).
• Psychiatric/neurologic effects: Rare agitation, mood changes, or seizures-more often a concern with overdose or interacting meds.
• Photosensitivity and rash: Use sunscreen and protective clothing if you’re sun-sensitive.

Serious risks (why supervision matters)

• Heart rhythm changes: QT prolongation can trigger dangerous arrhythmias, especially if you already have a prolonged QT, low potassium/magnesium, or take other QT-prolonging drugs.
• Retinal toxicity: A long-term risk tied to cumulative exposure. It’s more of an issue with chronic use (years), but baseline eye exams are smart if a clinician expects extended therapy.
• Overdose: A medical emergency. Early signs can include vomiting, dizziness, blurred vision, and low blood pressure, followed quickly by seizures, cardiac arrest, and severe hypokalemia. In children, a small number of tablets can be fatal-store it like you would opioids: locked away.

Drug interactions that deserve respect

• QT-prolongers: Macrolides (e.g., azithromycin), fluoroquinolones (e.g., levofloxacin), some antifungals, antipsychotics, methadone. Combining raises arrhythmia risk.
• Antacids and kaolin: Can reduce absorption. Separate by at least 4 hours.
• Cimetidine: Can increase chloroquine levels by reducing metabolism. Alternatives like famotidine don’t share this issue.
• Digoxin and cyclosporine: Levels may rise; monitoring may be needed.
• CYP2D6 interactions: Chloroquine can inhibit CYP2D6, potentially increasing concentrations of certain beta-blockers (e.g., metoprolol) and tricyclic antidepressants.
• Drugs that cause hypoglycemia: Insulins and sulfonylureas-watch blood sugars closely.

Who should be cautious or avoid it

• Known QT prolongation, history of serious ventricular arrhythmia, or uncorrected low potassium/magnesium.
• Preexisting retinal disease or a history of 4-aminoquinoline-related eye toxicity.
• Severe psoriasis (may worsen flares).
• Seizure disorders-use caution and review interacting drugs that lower seizure threshold.

Pregnancy and lactation

• Pregnancy: CDC and WHO consider chloroquine acceptable for malaria prophylaxis and treatment in pregnancy where it’s effective. The risk of malaria to the fetus is significant, so prevention matters.
• Breastfeeding: Generally considered compatible at standard doses; breast milk levels are low. It does not protect the infant-babies need their own dosing if indicated.

Monitoring, if you’ll be on it more than briefly

• Baseline EKG: Consider if you have cardiac risk factors or take QT-prolonging meds.
• Eye exam: If long-term use is expected (rare for travelers), get baseline and periodic screening.
• Labs: Clinicians might check electrolytes if you’re ill, dehydrated, or on diuretics, and blood glucose if you have diabetes.

Safety checklist before starting

• Destination confirmed as chloroquine-sensitive via current CDC/WHO guidance.
• Medication list reviewed for QT-prolongers and key interactions.
• Pregnant or trying to conceive? Confirm the plan with your clinician.
• Glucose-6-phosphate dehydrogenase (G6PD) status checked if you’ll need primaquine/tafenoquine for P. vivax/ovale relapse prevention.
• Clear plan on dosing by base vs salt and what to do if you miss a dose.
• Drug stored securely, away from children and pets.

Alternatives, decisions, and real-world scenarios

Most travelers won’t use chloroquine because resistance is common. Picking the right antimalarial is a match-up between your destination, medical history, schedule, and tolerance for side effects.

Decision criteria that simplify the choice

• Destination resistance: If chloroquine resistance exists, rule it out.
• Timing: Leaving in 2 days? Doxycycline and atovaquone-proguanil can be started close to departure; chloroquine and mefloquine prefer 1-2 weeks lead time.
• Heart risk: Long QT or multiple QT-prolonging meds pushes you away from chloroquine and mefloquine.
• Sun exposure: If you’ll be outdoors nonstop, doxycycline’s sun sensitivity might be a headache.
• Pregnancy: Chloroquine or mefloquine are options; avoid doxycycline and tafenoquine. Atovaquone-proguanil lacks robust pregnancy safety data.
• G6PD status: Needed before tafenoquine or primaquine.

Quick comparison (simplified)

Scenarios you might recognize

• Haiti or another chloroquine-sensitive spot: Weekly chloroquine can make sense. Confirm current sensitivity status right before travel-these maps change.
• Last-minute departure to sub-Saharan Africa: Skip chloroquine; pick atovaquone-proguanil or doxycycline depending on your health profile.
• Pregnant in second trimester, heading to an endemic area: If destination is chloroquine-resistant, mefloquine is often chosen; if sensitive, chloroquine may be considered. This is a shared decision with your obstetrician.
• History of long QT: Prefer atovaquone-proguanil or doxycycline; avoid chloroquine and other QT-prolongers if possible.
• Chronic P. vivax exposure (long stay in Asia or the Americas): Discuss relapse prevention (radical cure) with primaquine or tafenoquine and ensure a quantitative G6PD test first.

COVID-19 myth-busting in one breath

• Multiple large, well-run trials showed no benefit for treatment or prevention.
• Guidelines from NIH (updated 2024) and WHO advise against using chloroquine/hydroxychloroquine for COVID.
• If someone sells you chloroquine as a COVID cure, that’s a red flag.

Mini-FAQ

• Can I buy chloroquine online? Only from a legitimate pharmacy with a valid prescription. Avoid aquarium or “research” products-different purity, wrong dosing, and proven harm cases.
• Do I need chloroquine if I’m sleeping under a bed net? Nets and repellents reduce bites; antimalarials reduce your risk of severe disease if you’re infected. You want both in risk areas.
• What if I miss a weekly prophylaxis dose? Take it as soon as you remember. If it’s close to the next dose, just take that next dose-don’t double up. Keep the 7-day spacing going.
• Is alcohol a problem? Moderate alcohol doesn’t directly interact, but dehydration and electrolyte issues can raise arrhythmia risk if you already have heart vulnerabilities.
• Do I need an eye exam for a 3-week trip? Not typically. Eye exams matter if long-term use is expected; your clinician may still check your baseline history.
• How long do I keep taking it after I leave? Four weeks for chloroquine (and doxycycline). Atovaquone-proguanil is just 7 days after leaving.

Next steps and troubleshooting

• Trip booked, destination unclear about resistance: Check the latest CDC country pages or WHO guidelines with your clinician. Do this close to your departure date in case recommendations changed.
• Side effects after your first dose: For mild nausea or itch, try taking it with food and at night. If you get severe dizziness, palpitations, fainting, vision changes, or hypoglycemia symptoms, seek care immediately.
• Pharmacy says chloroquine is back-ordered: Ask about switching to an appropriate alternative (often atovaquone-proguanil or doxycycline), given your destination.
• You develop a fever during travel or within a month after return: Treat it like an urgent issue and tell the clinic you’ve been in a malaria area. Early testing and treatment save lives.
• You’re planning months in a malaria region: Consider adherence (weekly vs daily), sun exposure, and long-term tolerability. Ask about standby emergency treatment only if recommended for your specific itinerary and after training on when to use it.

What gives this guidance teeth

These points line up with primary sources clinicians rely on: the CDC Yellow Book (2024-2025) for travel medicine, WHO Guidelines for Malaria (2023 updates), and the U.S. FDA’s chloroquine phosphate label (revised 2024). The COVID conversation shifted years ago with the RECOVERY and WHO Solidarity trials; national bodies like NIH and WHO now converge on clear advice against chloroquine for COVID-19. If you remember nothing else, remember this: match the drug to the map, respect the heart and eye risks, and don’t wing the dose.