Antivirals work in a couple of ways that can prevent the virus from spreading once inside you or by preventing infection from ever taking hold

• Antiviral drugs treat viral infections like the flu, shingles, and HPV.
• Antivirals work in a few ways either by preventing infection entirely or reducing further spread of the infection once you're sick.
• You can only get antiviral medication through a prescription.
• This article was medically reviewed by Tania Elliott, MD, who specializes in infectious diseases related to allergies and immunology for internal medicine at NYU Langone Health.
• Visit Insider's Health Reference library for more advice.

While antiviral drugs can't help with bacterial infections like strep throat, they can combat viral infections including the flu, shingles, or HPV. In this article, we discuss how antiviral drugs work, how to get them, and what to consider before taking an antiviral medication.

Antivirals work to prevent viral infection and spread

Antivirals treat infections by preventing the virus from spreading throughout your body. In other words, they don't kill the virus, outright, which makes developing antivirals tricky.

"We have to find ways to fool or cheat the virus so that it doesn't multiply," says Jagdish Khubchandani, MBBS, PhD, a professor of health science at Ball State University. An antiviral drug can help prevent or treat infections in several ways.

1. Prevent a viral infection from taking hold.

A virus, like influenza, first needs to attach to human cells before it can infect you and spread. Antiviral drugs can trick the virus into attaching to the medication instead of your cells and therefore prevent infection entirely.

2. Interfere with the virus' ability to reproduce.

Once inside a human cell, the virus takes over and starts making copies of itself. The more copies it makes, the more infected, and usually sicker, you become. Antivirals disrupt this process inside the cell to prevent the virus from reproducing, which can reduce the severity of your symptoms as well as speed up your recovery.

How quickly the antiviral is able to work depends on the drug. "For many antiviral drugs, you can see [an] effect starting after 48 hours," says Khubchandani.

3. Prevent the virus from spreading throughout the body.

After a virus has turned your cells into virus-producing factories, it'll release all of those copies, which then will hitch a ride in your bloodstream. Antivirals halt the spread by preventing the initial release of viral particles from your cells. Antivirals like Relenza, which fights the flu, work this way.

Creating new antiviral drugs

"Most antiviral drugs act on specific viruses, which means each time we have a new type of infection, we may need a new type of drug," says Khubchandani. That makes it tough to have a common set of ingredients, he says.

Moreover, viruses are constantly mutating and adapting to threats. That's why we have to have a new flu shot made each year.

Creating a new antiviral is not an easy or quick process, either. And there are a variety of reasons why, including the years of research it takes, the clinical trials and approvals needed, and even the time to market the new medication, says Khubchandani.

For example, the antiviral acyclovir, which treats herpes and chickenpox, was patented in 1974. Clinical trials took place from 1977-78. And clinical use was finally approved in 1981.

How to get an antiviral drug

Antiviral drugs are only available via prescription. However, Tamiflu may become available over the counter in the future.

Antivirals may interact with other medications, such as medications that help with:

• Sleep
• Lowering cholesterol
• Bacterial infections, aka antibiotics
• Fighting viruses (ie. other antivirals)

So it's important to tell your doctor what other medications you're on. Moreover, if you're on birth control, certain antivirals to treat HIV could have an interaction and reduce the birth control's effectiveness, says Khubchandani. But it depends on the type of birth control and antiviral, so it's best to discuss options with a doctor.

Who should and shouldn't take antivirals

While children, pregnant women, people who are immunocompromised, and those with multiple chronic conditions can still be prescribed antivirals, they should be careful, says Khubchandani.

For instance, "some antiviral drugs can travel from mothers' milk to babies, where side effects can be severe or unknown due to lack of research," he says.

Research on how antivirals affect these groups is often limited — and conducting the research can be risky in an already high-risk population, says Khubchandani. Take Valtrex, for example.

Valtrex is used primarily to treat herpes infections. However, there's not enough on the effects of the drug during pregnancy. Therefore, whether or not a pregnant woman should take it should be discussed with her doctor.

Overall, whether or not an antiviral is the right course of treatment will depend on the individual.

"Each person is unique — disease type, health profile, blood markers, to check for liver and kidney function, and several other factors ... have to be considered before prescribing," says Khubchandani.

Related stories from Health Reference:

• The difference between bacteria and viruses, and how to prevent their spread
• Antibiotic resistance is a dangerous consequence of our tendency to overuse drugs
• Antibiotics treat infections by either killing or sterilizing bacteria