HIV Treatment

Drug Resistance

Last Reviewed: March 31, 2025

Key Points

  • HIV mutations sometimes develop while a person is taking HIV medicines, which may cause drug-resistant HIV that can be transmitted to other people.
  • Once drug resistance develops, HIV medicines that previously controlled a person’s HIV are no longer effective. In other words, the HIV medicines cannot prevent the drug-resistant HIV from multiplying, causing the treatment to fail.
  • By identifying which, if any, HIV medicines will not be effective against HIV, drug resistance testing can help determine which HIV medicines to include in an HIV treatment regimen.
  • Taking HIV medicines exactly as prescribed reduces the risk of drug resistance.

 

What is HIV drug resistance?

As HIV multiplies in the body, it sometimes changes form, known as a mutation. Some HIV mutations can cause resistance to HIV medicines (called HIV drug resistance), which means that the virus will be resistant to all or some parts of a prescribed HIV medicine.

In some cases, HIV drug resistance can reduce the effectiveness of multiple drugs in a class of HIV medicines. For example, resistance to the nucleoside reverse transcriptase inhibitor (NRTI) emtricitabine can cause resistance to lamivudine or other NRTIs.

Drug resistance can develop over time in people with HIV or can be spread from person to person (called transmitted resistance), which includes perinatal transmission during pregnancy. This means that some people will have drug-resistant HIV even before they take HIV medicines.

For people who develop HIV drug resistance while taking HIV medicines, the original treatment regimen is unlikely to continue being effective. In other words, the original HIV medicines cannot prevent the drug-resistant HIV from multiplying, and the HIV treatment will fail unless a different treatment regimen is started.

On the other hand, people who acquire transmitted HIV resistance may not respond to certain treatment regimens, even if it is their first time taking HIV medicines. To prevent HIV from multiplying due to an ineffective treatment regimen, it is important to receive drug resistance testing as soon as possible after receiving an HIV diagnosis.

What is drug-resistance testing?

Drug-resistance testing identifies which, if any, HIV medicines will not be effective for a person with HIV. Drug-resistance testing evaluates resistance to common drug classes (such as protease inhibitors) using a sample of blood.

People with HIV should start taking HIV medicines as soon as possible after an HIV diagnosis. However, drug-resistance testing is usually performed before a person starts taking HIV medicines. Drug-resistance test results help determine which HIV medicines to include in a person’s first HIV treatment regimen.

Once HIV treatment is started, a viral load test is used to monitor whether the HIV medicines are working effectively. If viral load testing indicates that a person’s HIV treatment regimen is not effective, drug-resistance testing is repeated. The test results can identify whether drug resistance is the problem and, if so, can be used to select a new HIV treatment regimen.

How can a person taking HIV medicines reduce the risk of drug resistance?

Taking HIV medicines exactly as prescribed (called medication adherence) reduces the risk of drug resistance. Even occasionally skipping HIV medicines can allow HIV to multiply, which increases the risk that the virus will mutate and produce drug-resistant HIV.

Before starting HIV treatment, people with HIV should tell their health care provider about any issues that can make medication adherence difficult. For example, a busy schedule or lack of health insurance can make it hard to take HIV medicines consistently. Read the HIVinfo fact sheet HIV Treatment Adherence for a list of other common causes of poor medication adherence.

Health care providers can help find a suitable treatment regimen that increases the likelihood of medication adherence and reduces the risk of drug resistance.

For people who are actively engaging in sexual activity, the risk of transmitted drug resistance can be significantly reduced if their partner(s) take pre-exposure prophylaxis (PrEP). PrEP nearly eliminates the risk of sexual HIV transmission for partners, including the transmission of drug-resistant HIV. PrEP offers protection in the event of unnoticed or unexpected drug resistance.

The following HIVinfo resources offer more information on drug resistance and medication adherence:

This fact sheet is based on information from the following sources:

From the HIV Clinical Practice Guidelines at Clinicalinfo.HIV.gov:

From the Department of Veterans Affairs:

From the National Institute of Allergy and Infectious Diseases:

Also see the HIV Source collection of HIV links and resources.