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An antiviral is a medicine used to treat or prevent certain viral infections. Antivirals work by slowing a virus or blocking steps it needs to copy itself. Each antiviral targets specific viruses, so one antiviral does not work for every viral illness. These medicines are used only when the virus, timing, and patient risk fit the treatment plan.
read more about antiviral ...Viruses use human cells to make more copies of themselves. Antivirals interfere with steps in that process, such as viral entry, enzyme activity, genetic copying, or viral release from infected cells. This can reduce viral spread in the body. Antivirals do not work the same way as antibiotics because antibiotics target bacteria, not viruses.
Antivirals are used for infections such as influenza, herpes, HIV, hepatitis B, hepatitis C, COVID-19, shingles, and chickenpox. Some are used for short courses, while others are taken long term for chronic viral infections. Timing can affect results, especially with flu and COVID-19 treatments that work best early in illness. A clinician can decide whether testing, risk level, and symptom timing support antiviral treatment.
Common antivirals include acyclovir, valacyclovir, oseltamivir, zanamivir, baloxavir, remdesivir, nirmatrelvir-ritonavir, entecavir, tenofovir, sofosbuvir-based regimens, and antiretroviral medicines for HIV. The selected medicine depends on the virus and the patient's kidney function, liver function, pregnancy status, and drug interactions. Some antivirals prevent complications rather than fully curing the infection. Patients should follow the exact dosing schedule because missed doses can reduce effectiveness.
Antiviral side effects vary by medicine. Possible effects include nausea, diarrhea, headache, fatigue, dizziness, kidney strain, liver enzyme changes, or drug interactions. Some antivirals interact strongly with heart medicines, seizure medicines, cholesterol medicines, and immune-suppressing medicines. Seek medical care for severe allergic reaction, confusion, worsening shortness of breath, yellowing skin or eyes, very low urine output, or severe weakness.
No, antivirals treat selected viral infections. Bacterial infections require different medicines, such as antibiotics, when treatment is needed.
No, each antiviral works against specific viruses. Some viral infections have no antiviral treatment, and some antivirals reduce severity rather than fully remove the virus.
Some antivirals work best when started early, before the virus has spread widely in the body. This is why flu and COVID-19 treatments have time-sensitive windows.
Some antivirals can be used for prevention after exposure or in high-risk situations. This depends on the virus, exposure type, and clinician guidance.
Antiviral Medication: What It Is & How It Works. Cleveland Clinic. https://my.clevelandclinic.org/health/treatments/antivirals. Date Accessed June 3, 2026.
Treating Flu with Antiviral Drugs. Centers for Disease Control and Prevention. https://www.cdc.gov/flu/treatment/antiviral-drugs.html. Date Accessed June 3, 2026.
Oseltamivir: MedlinePlus Drug Information. MedlinePlus. https://medlineplus.gov/druginfo/meds/a699040.html. Date Accessed June 3, 2026.
Oseltamivir Oral Route. Mayo Clinic. https://www.mayoclinic.org/drugs-supplements/oseltamivir-oral-route/description/drg-20067586. Date Accessed June 3, 2026.
A Review: Mechanism of Action of Antiviral Drugs. PMC. https://pmc.ncbi.nlm.nih.gov/articles/PMC7975490/. Date Accessed June 3, 2026.