References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
HIV drug resistance occurs when the virus mutates in ways that reduce the effectiveness of antiretroviral medications. This can happen when HIV treatment isn’t taken consistently, when drug levels in the body are too low, or when someone is infected with an already-resistant strain. Understanding resistance helps explain why adherence to treatment is so important and why your doctor monitors your viral load regularly.
How Does HIV Resistance Develop?
HIV replicates rapidly, producing billions of new copies daily. Each replication cycle carries a risk of genetic mutation. Most mutations are harmless or even harmful to the virus. But occasionally, a mutation allows the virus to survive in the presence of a drug that would normally suppress it.
If drug levels are inconsistent (due to missed doses, poor absorption, or drug interactions), the virus can replicate enough to accumulate these resistance mutations. Once resistant variants dominate, that drug no longer works.
Types of Resistance
| Type | How It Happens | Implication |
|---|---|---|
| Acquired resistance | Develops during treatment, usually from poor adherence | The drug(s) must be changed |
| Transmitted resistance | Infected by a partner who has drug-resistant HIV | Some drugs may not work from the start |
| Cross-resistance | Resistance to one drug extends to related drugs in the same class | May lose an entire drug class |
How Is Resistance Tested?
Resistance testing (genotypic or phenotypic) analyses the genetic sequence of your HIV to identify mutations associated with drug resistance. In the UK, resistance testing is standard practice:
- At diagnosis: Before starting treatment, to check for transmitted resistance
- At treatment failure: If viral load becomes detectable after being suppressed
- Before switching drugs: To ensure the new regimen will be effective
How to Prevent Resistance
- Take your medication every day at the same time — this is the most important thing
- Don’t skip doses — even occasional missed doses create windows for resistance to develop
- Tell your doctor about side effects — they can switch you to a better-tolerated drug rather than you stopping on your own
- Avoid drug interactions — some medications and supplements can reduce ART levels
- Attend clinic appointments — regular viral load monitoring catches problems early
Modern integrase inhibitor-based regimens (dolutegravir, bictegravir) have a high barrier to resistance, meaning it takes many mutations for the virus to become resistant. This is one reason they’re preferred as first-line treatment.
Read more: What is HIV? | Starting HIV treatment | ART side effects
Frequently Asked Questions
If I develop resistance, can I still be treated?
Yes. There are multiple drug classes and many individual drugs available. Your doctor will use resistance testing to find a combination that your virus is still sensitive to. Very few people exhaust all treatment options.
Can I pass resistant HIV to a partner?
If your viral load is detectable and you have resistant HIV, you can transmit the resistant virus. If your partner becomes infected, the same drugs may not work for them. This is called transmitted resistance. Maintaining an undetectable viral load prevents all transmission (U=U).
Does everyone on HIV treatment develop resistance?
No. People who take their medication consistently and maintain an undetectable viral load are very unlikely to develop resistance. Resistance is primarily a risk with poor adherence or suboptimal drug regimens.
Related reading
- Injectable HIV Treatment: Everything You Need to Know
- Are HIV Tests Accurate If You're on PrEP, PEP or ART?
- CD4/CD8 Ratio: What It Means and Why It Matters
- CD4 Counts Explained: What Your Numbers Mean
- Changing HIV Treatment: When, Why and How
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
