Antiviral medication: what they do and how to use them

Some viral illnesses respond well to pills — but only if you act right. Antiviral drugs don’t magically kill every virus. They slow viral replication so your immune system can catch up. That small difference changes when and how you should use them.

Quick facts: common antivirals and what they treat

A few antivirals you’ll hear about often: acyclovir and valacyclovir for herpes (cold sores, genital herpes); oseltamivir (Tamiflu) and zanamivir for flu; nirmatrelvir/ritonavir (Paxlovid) and molnupiravir for early COVID in high-risk people; and remdesivir for hospitalized COVID patients. Each drug targets a different step of the virus life cycle — some stop copying the virus, others block enzymes the virus needs.

Timing matters. For flu, antivirals work best within 48 hours of symptoms starting. For herpes, early treatment shortens outbreaks. For COVID, some oral antivirals are meant for people at higher risk and must start within a few days of symptoms. If you wait too long, the benefit drops.

How to use antivirals safely

Ask your doctor if an antiviral is right for you — and be honest about medical history and other drugs you take. Some antivirals affect the liver or kidneys, so older adults and people with chronic illnesses may need dose changes. Ritonavir, used to boost some COVID pills, interacts with many common meds — always check with a pharmacist.

Follow the full dose schedule. Stopping early can let the virus rebound or raise resistance risk in some cases. Stay hydrated and report side effects such as severe nausea, rash, new confusion, or trouble breathing right away.

Buying antivirals online? Make safe choices. Pick licensed pharmacies that ask for a prescription and show full contact details. Avoid sites that sell prescription drugs without any prescription or pressure you with huge discounts. When your package arrives, check the pill appearance, expiry date, and consult a pharmacist if anything looks off.

Resistance is real but avoidable. Use antivirals only when indicated and follow dosing instructions. In immune-suppressed people, resistant virus can develop faster, so care teams may use different drugs or IV options.

Short checklist before you start an antiviral: do you have a clear diagnosis? Can you start treatment within the recommended window? Do you have kidney or liver issues? Are you on other medicines that interact? If any answer is unclear, call your prescriber or pharmacist.

If you want a quick next step: keep photos of your meds, save the pharmacy phone number, and ask your provider whether antiviral treatment will change your recovery timeline. Want help finding reliable online pharmacies or specific drug info? Our site has guides that walk you through safe buying and what to expect from each antiviral.