acyclovir vs oseltamivir
Side-by-side comparison of acyclovir and oseltamivir Data from FDA drug databases (Orange Book, NDC Directory, recalls, shortages) covering 20,000+ approved drugs, plus CMS pricing; see our methodology.
Zovirax
Tamiflu
Acyclovir is an antiviral medicine. It is used to treat infections caused by certain viruses.
Oseltamivir (Tamiflu) is an antiviral medicine. It helps treat and prevent the flu (influenza A and B).
Acyclovir is used to treat shingles, which is caused by herpes zoster. It also treats genital herpes, both the first time you have it and when it comes back. Acyclovir can also treat chickenpox.
This medicine treats the flu in people 2 weeks and older who have had symptoms for no more than 48 hours. It can also prevent the flu in people 1 year and older. Remember that this medicine is not a substitute for your yearly flu shot. It's important to get vaccinated every year.
Acyclovir stops the virus from growing and spreading. It does this by interfering with the virus's ability to make copies of itself. This helps your body fight off the infection.
Oseltamivir stops the flu virus from spreading in your body. It does this by blocking a protein on the virus called neuraminidase. This helps you get better faster or prevents you from getting sick.
- • Malaise (feeling unwell)
- • Nausea
- • Diarrhea
- • Nausea
- • Vomiting
- • Headache
- • Pain
- Tiredness 7,612
- Diarrhea 7,064
- Using the medicine for something it's not approved for 5,797
- Lung infection 5,474
- Feeling sick to your stomach 5,330
- Off Label Use 1,776
- Drug Ineffective 712
- No Adverse Event 582
- Vomiting 444
- Nausea 443
Acyclovir can cause nervous system problems, especially in older adults or people with kidney problems. Tell your doctor if you have kidney problems before taking this medicine.
Rarely, this medicine has been linked to serious skin reactions and allergic reactions. Stop taking this medicine and get medical help right away if you have signs of an allergic reaction or a severe skin rash. Some people, especially children, may experience confusion or unusual behavior while taking this medicine. Watch for any changes in behavior and tell your doctor right away.
Tell your doctor if you are pregnant or plan to become pregnant. It is not known if acyclovir will harm an unborn baby. Talk to your doctor about the risks and benefits of taking acyclovir while breastfeeding.
Tell your doctor if you are pregnant or plan to become pregnant. Studies suggest this medicine does not increase the risk of birth defects. Talk to your doctor about the risks and benefits of taking this medicine while pregnant or breastfeeding.
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How to Read This acyclovir vs oseltamivir Comparison
acyclovir is classified in the Antiviral (Nucleoside Analog) drug class, while oseltamivir sits within the Neuraminidase Inhibitor (Antiviral) class. Drugs from different classes work through distinct mechanisms, so a head-to-head comparison illustrates trade-offs rather than equivalence. Both drugs are prescription-only, so a licensed provider must authorize use.
Adverse event totals above are pulled from the FDA's Adverse Event Reporting System (FAERS). For these top-ranked reactions alone, acyclovir has 31,277 submissions while oseltamivir has 3,957. Those figures reflect cumulative reporting volume — not per-patient risk — so older, widely dispensed drugs typically look worse on count alone. No direct interaction between these two drugs is listed in our FDA-derived dataset, though co-prescription still warrants pharmacist review. Serious warnings, pregnancy guidance, and contraindications can differ even when indications overlap.
A table cannot substitute for clinical judgment. Effectiveness, tolerability, drug-drug interactions with your other medications, kidney and liver function, pregnancy status, insurance formulary, and price all feed into a decision that only a licensed prescriber can make responsibly. Data here is sourced from FDA Structured Product Labels (SPL) and FAERS, both of which update as manufacturers and clinicians submit new information. This page is for educational purposes only, is not medical advice, and should not be used to self-switch between acyclovir and oseltamivir — always consult your physician or pharmacist first.
Important: This comparison is for informational purposes only. Drug effects vary between individuals. Always consult your doctor or pharmacist for personalized medical advice.