An antiviral is a medicine designed to fight viruses, the tiny infectious agents that cause diseases like the flu, chickenpox, and the common cold. Unlike antibiotics, which kill bacteria, antivirals work specifically against viruses by stopping them from multiplying inside your body's cells.

When you get sick with a virus, antivirals can help you recover faster and feel less miserable. For example, if you catch the flu early enough, your doctor might prescribe an antiviral medication like Tamiflu to shorten how long you're sick. Some antivirals prevent viruses from entering your cells in the first place, while others stop viruses from making copies of themselves once they're already inside.

The word can also be used as an adjective to describe anything that fights viruses: antiviral drugs, antiviral properties, or antiviral treatments. Scientists discovered that some natural substances have antiviral effects, meaning they can slow down or stop certain viruses from spreading.

Creating antivirals is tricky because viruses hijack your own cells to reproduce, so scientists have to find ways to stop the virus without harming your healthy cells. That's why we have effective antivirals for some diseases but not others. Researchers continue working to develop new antivirals for viruses that currently have no good treatments.