HIV is a treatable condition, but sometimes, a person’s medication stops working. It is important to know when this happens so that they can try a different treatment regimen.

While there is no cure for HIV, treatment known as antiretroviral therapy (ART) can help reduce the risk of virus transmission while allowing people with HIV to live long and healthy lives.

In many cases, ART prevents a person from ever developing AIDS. ART controls a person’s viral load by preventing HIV particles from multiplying.

ART can work so well that the virus is undetectable in testing. At this stage, HIV is not transmissible through sex. People commonly refer to this as “undetectable = untransmissible (U=U).”

However, ART sometimes stops working. The medication is no longer able to suppress the virus, and a person’s viral load starts to increase.

This article discusses how common it is that HIV treatment stops working, possible reasons, and signs to look out for.

Research provides mixed results about the prevalence of HIV treatment failure.

A 2023 review of 81 studies between 2007 and 2022 found that ART treatment failure rates ranged from 0–42.65%.

One study from 2018 found that HIV treatment failure occurred at a rate of 20.3%.

This study also found that the immunological failure — suppression of immune cells called CD4+ — occurrence was 13.2%, and the virological failure — inability to maintain suppression of HIV RNA — occurrence was 14.7%.

The duration of ART treatment among the study participants ranged from 6 months to 12 years.

According to the World Health Organization (WHO), up to 10% of adults can experience drug resistance to the drug class known as non-nucleoside reverse transcriptase inhibitors (NNRTIs).

A common reason for HIV treatment failure is drug resistance.

The WHO and National Institutes of Health list several factors that contribute to HIV drug resistance:

  • HIV genetic structure changes
  • the emergence of drug-resistant HIV strains
  • previous exposure to antiretroviral drugs
  • being born to a birthing parent who has HIV
  • not taking medication as prescribed

The reasons why a person stops taking medication include:

  • cost and affordability
  • intolerable side effects
  • mental health issues
  • substance use disorders
  • fear of stigma

Stopping and restarting treatment, sometimes referred to as “treatment holidays,” can also contribute to HIV drug resistance.

ART treatment failure can also result from:

  • issues with medication absorption
  • drug interactions
  • inadequate dosing

There are several ways a person can tell whether their HIV treatment has stopped working.

Viral load test

A viral load test is a measurement of the amount of HIV present in a sample of blood.

There are several types of viral load tests.

Their functions include:

  • diagnosing acute HIV infection
  • guiding treatment decisions
  • monitoring treatment efficacy

To monitor treatment, doctors order viral load tests at regular intervals, 3–6 months apart.

Possible results include:

  • Negative or undetectable: This is a sign that the HIV medications are working so well that the level of HIV in a person’s blood is too low for the test to detect. A person must continue taking their medication as prescribed even with this test result.
  • Low viral load: This means the medications are working well enough to stop the infection from worsening.
  • High viral load: This is a sign that the HIV treatment has stopped working, and a doctor will need to change the treatment plan.

Sometimes, there can be a small increase in the viral load, known as a blip. This happens when the viral load becomes briefly detectable and later returns to undetectable. Doctors have found this to be a common occurrence. Taking medications every day can help prevent blips.

CD4 cell count

CD4 T lymphocytes are immune system cells. HIV targets these cells, enters them to replicate, and then kills them. The immune system tries to create more CD4 cells to compensate but eventually cannot keep up.

Ineffective or absent HIV treatment can cause decreased CD4 levels as the HIV viral load increases.

Clinicians use CD4 counts to stage HIV and to monitor treatment effectiveness.

Proliferative HIV is not the only factor that can decrease CD4 levels. Other causes may include:

CD4 counts are measured as cells per microliter. A range of 500–1,500 is considered typical in people without HIV.

A count of below 200 is one of the criteria for the definition of AIDS used by the Centers for Disease Control and Prevention (CDC).

Flu-like symptoms

When HIV treatment has stopped working, a person’s viral load increases and can cause flu-like symptoms.

These include:

  • fever
  • chills
  • joint pain
  • fatigue
  • sore throat
  • headaches
  • muscle aches
  • swollen lymph nodes

To determine whether symptoms are from an increasing HIV viral load or another infection, such as the flu, a person can contact a doctor for testing.

HIV treatment aims to suppress viral load. With effective treatment, a person with HIV can live a long and healthy life without developing AIDS.

This treatment can sometimes stop working, which is often due to drug resistance. Identifying treatment failure allows a person’s doctor to prescribe a new medication regimen.