Every year in the UK thousands of people are diagnosed with HIV, despite major advances in prevention and treatment. In 2024 there were around 3,043 new HIV diagnoses across the UK, representing a 4% drop from the year before. Yet even with this progress, nearly 42% of diagnoses in England were made at a late stage* of infection – when the virus has already caused significant damage to the immune system.
That’s why tools like pre-exposure prophylaxis (PrEP) matter now more than ever. PrEP gives people who are HIV-negative an effective way to protect themselves before any exposure occurs – shifting the story from reactive to proactive.
In this article, we’ll explore what PrEP is, how it works, who it’s for, and why it has the potential to reshape HIV prevention in the UK.
*The definition of late HIV diagnosis currently used in England is a CD4 count below 350 within 91 days of diagnosis.
Contents
- How HIV Affects the Body: Understanding Its Impact on the Immune System
- What Is PrEP and How Does It Work?
- What PrEP Is Currently Available?
- Who Might Consider Taking PrEP?
- Does PrEP Have Any Side Effects?
- PrEP Monitoring: Tests and Check-Ups You’ll Need While Taking It
- Introducing the PrEP Injection (Cabotegravir): The New HIV Prevention Jab
- What Does U=U Mean?
- Key Takeaways About PrEP
DISCLAIMER:
While I am a practising doctor, the information on this site is for educational purposes only. It does not take into account your personal circumstances, which can significantly affect medical decision-making and treatment. This content therefore does not constitute medical advice, and should not be relied upon for diagnosis or treatment. Always consult a qualified healthcare provider regarding any health concerns.
This article was written on the 20/10/2025 using up-to-date sources at that time. Please be aware that medical information and guidelines change often.
How HIV Affects the Body: Understanding Its Impact on the Immune System
HIV is a type of viral infection that affects the immune system, and in turn, the body’s ability to fight infections. If left untreated, it can progress to Acquired Immunodeficiency Syndrome (AIDS) – this is a late stage of HIV infection, where the immune system is badly damaged. Infections at this stage can be life-threatening.
HIV is spread through bodily fluids – such as through unprotected sexual contact (anal, vaginal, or, rarely, oral sex), sharing drug injecting equipment, or from mother to child during pregnancy, birth, or breastfeeding if untreated.
When HIV enters the body, it targets specific immune cells called CD4 cells. The virus uses these cells to make copies of itself, destroying them in the process. Over time, this weakens the immune system and makes it harder to fight off infections.
Without treatment, HIV progresses through three main stages:
- Acute HIV infection – This happens 2-4 weeks after exposure. Some people experience flu-like symptoms (fever, sore throat, swollen glands, rash) as the body reacts to the virus.
- Chronic HIV infection – The virus remains active but reproduces at low levels. Many people may not feel ill during this time, but HIV continues to damage the immune system. The length of this phase varies, but on average is between 8-10 years.
- AIDS (Acquired Immunodeficiency Syndrome) – The most advanced stage of HIV, when CD4 count falls below 200 cells/mm3. The immune system becomes so weakened that the body can no longer fight off common infections or diseases.
At this stage, people become vulnerable to opportunistic infections – illnesses that take advantage of a weakened immune system. These can include:
- Tuberculosis (TB)
- Pneumocystis pneumonia (PCP)
- Candidiasis (thrush) of the oesophagus or lungs
- Toxoplasmosis, a brain infection caused by a parasite
- Certain cancers, such as Kaposi’s sarcoma or lymphoma
Without treatment, these infections can become life-threatening. However, with modern HIV treatment (antiretroviral therapy), people living with HIV can live long, healthy lives – and with prevention tools like PrEP, many can avoid infection altogether.
What Is PrEP and How Does It Work?
PrEP refers to taking anti-retroviral therapy to reduce the risk of acquiring Human Immunodeficiency Virus (HIV). When taken correctly, it is 99% effective at preventing transmission.
Tablet PrEP contains medicines that block the enzyme HIV needs to replicate – reverse transcriptase. So, even if HIV enters the bloodstream, it can’t make new copies or establish a long-term infection.
In the case of the new injectable PrEP (Cabotegravir), the mechanism is slightly different – it blocks another viral enzyme called integrase, preventing HIV from inserting its genetic material into human DNA. The result is the same: HIV can’t multiply or spread.
Why PrEP Matters for HIV Prevention
PrEP matters because it gives people the power to prevent HIV before exposure – safely, effectively, and without stigma. For some, condom use may not always be possible or reliable; for others, PrEP represents a way to reclaim control over their health. It helps reduce new HIV infections, narrow health inequalities, and empower people to protect themselves on their own terms.
What PrEP Is Currently Available?
Since becoming readily available on the NHS in the UK, PrEP has taken the form of a tablet that can be taken in the following ways according to BASHH/BHIVA* guidance:
- Continuously – one tablet taken daily. You need to take it continuously for 7 days to be protected in this way.
- On demand dosing (or “2:1:1” dosing) – two tablets are taken 2-24 hours before potential exposure, and one tablet taken at 24 hours and 48 hours. You then carry on taking one tablet daily until you’ve not had sex for two days. This is only recommended for anal sex. It also can’t be taken if you have hepatitis B, as starting/stopping PrEP can make the virus more active.
- “2:7” dosing – two tablets are taken 2-24 hours before potential exposure and one tablet daily for 7 days following
- TTSS dosing – where four oral doses are taken each week
A single tablet typically contains two drugs – Tenofovir and Emtricitabine. These medications are also used to treat HIV.
It should generally be taken with or after food. If you’re sick within an hour of taking it, you should take another tablet.
Last week, the first injectable form of PrEP was announced for rollout across England and Wales — following Scotland, which approved its use in February 2025. More on this below.
*BASHH/BHIVA = British Association for Sexual Health and HIV/British HIV Association
How Can You Get PrEP on The NHS?
You can access PrEP free of charge through NHS sexual health clinics. You can find your nearest sexual health clinic on the NHS website by clicking here.
You can also pay for PrEP privately through online pharmacies such as Superdrug Online Doctor.
PrEP became available for free on the NHS in Scotland in 2017, with NHS England trialling it in 2017 before making it routinely available to all in 2020.
Who Might Consider Taking PrEP?
PrEP is recommended for people who are HIV-negative but at higher risk of HIV exposure.
You might consider PrEP if you are:
- A gay, bisexual, or other man who has sex with men (GBMSM)
- A Black African man or woman
- A transgender woman
- A recent migrant from a country where HIV is more common
- Someone who injects drugs or has shared injecting equipment
- Someone involved in sex work or transactional sex
You might also benefit from PrEP if you:
- Have condomless sex with partners whose HIV status is unknown or untreated
- Take part in group sex or chemsex
- Have recently had another sexually transmitted infection (STI) or used post-exposure prophylaxis (PEP)
- Travel frequently to and have sex with people from areas where HIV prevalence is high
- Live in situations where using condoms or negotiating safer sex is difficult – for example,
- due to alcohol or drug use,
- coercive or violent power dynamics in relationships, or
- housing or financial instability
If you’re unsure whether you might benefit from PrEP, this quick quiz by bepreped.co.uk can help.
Does PrEP Have Any Side Effects?
PrEP is well tolerated by many people. Around 1 in 10 people will experience mild nausea, diarrhoea, headache and bloating, but these symptoms usually improve after the first month. If it causes an upset stomach, taking it with or just after food might help.
It can also affect your kidney function, particularly if you’re aged over 50 or you already have kidney problems, and bone health, though this is rare.
PrEP Monitoring: Tests and Check-Ups You’ll Need While Taking It
Regular monitoring is essential to make sure PrEP is safe and effective, and makes sure any complications are picked up early.
Monitoring can include:
- HIV testing
- A blood test for HIV every 3-6 months – to confirm you remain HIV-negative before continuing PrEP
- Kidney function
- A blood test to check kidney function at least annually
- More frequent monitoring is needed if eGFR drops significantly, or if initial readings are slightly lower than normal
- Sexually Transmitted Infection (STI) screening
- Every 3 months, screen for chlamydia, gonorrhoea, and syphilis if you have new or multiple sexual partners
- Hepatitis B and C screening may be needed for GBMSM and others at higher risk
- Bone health
*DEXA scan = looks at how strong your bones are.
Introducing the PrEP Injection (Cabotegravir): The New HIV Prevention Jab
Until now, tablet PrEP has been the only option available on the NHS. Now, Cabotegravir, a long-acting injectable form of PrEP, is being rolled out across England and Wales – already available in Scotland since February 2025.
It is available as an alternative to oral PrEP for those who cannot take tablets, either due to medical or social reasons.
This comes as part of NHS England’s commitment to become the first country to end HIV transmissions by 2030.
How Often Is the HIV Prevention Injection Given?
Cabotegravir is given as an intramuscular injection every two months at sexual health clinics. It provides continuous protection without the need to take daily tablets.
Another drug, Lenacapavir, is in early clinical trials and may, in future, offer yearly dosing, making HIV prevention even easier.
Does the HIV Prevention Injection Have Side Effects?
As with any medication, there is the potential for side effects. These are some of the common potential side effects listed on the British National Formulary (BNF):
- Feeling tired or weak (asthenia, malaise)
- Headache or dizziness
- Nausea, diarrhoea, vomiting, or other stomach upset
- Muscle aches (myalgia)
- Fever or feeling hot
- Weight gain
- Anxiety, depression, or sleep disturbances
What Does U=U Mean?
I wanted to quickly talk about the phrase “U=U”, because it’s something we need to discuss more openly. It stands for Undetectable = Untransmittable.
Back in the 1980s, when HIV was first identified, it was almost unimaginable that someone living with HIV could have sex without passing the virus on. Today, thanks to modern treatment and prevention, a person who takes their medication correctly and achieves an undetectable viral load (so low it cannot be measured by standard tests) cannot transmit HIV to their sexual partners.
As long as treatment continues and the viral load remains undetectable, there is zero risk of sexual transmission, even without condoms.
U=U is supported by strong scientific evidence from major studies like the PARTNER study.
Key Takeaways About PrEP
- PrEP is a highly effective HIV prevention method, available free on the NHS.
- Tablet PrEP (Tenofovir + Emtricitabine) can be taken daily or around times of sexual activity.
- Injectable PrEP (Cabotegravir) is a new long-acting option given every two months.
- Monitoring includes regular HIV and kidney tests, as well as STI testing, and bone checks if needed.
- PrEP, anti-retroviral treatment, and post-exposure prophylaxis (PEP) together are transforming HIV prevention – protecting people living with and without HIV, and moving the UK closer to ending new HIV transmissions by 2030.
Beyond its clinical benefits, PrEP also helps challenge HIV stigma. It normalises proactive sexual health care and encourages open conversations about HIV testing and prevention – helping to create a society where HIV is treatable, preventable, and free from shame. And with continued awareness, equitable access, and innovation in treatments, the UK’s goal of ending new HIV transmissions by 2030 is not just ambitious – it’s achievable.
- How much did you know about PrEP before reading this article?
- What more could be done to make HIV prevention information accessible to everyone?
- Do you think the rollout of injectable PrEP will make prevention easier and more inclusive?
- How can we reduce stigma around HIV and sexual health conversations?
I’d love to hear from you! Please leave a comment down below.
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