How Effective Is PrEP at Preventing HIV?

By kduruike
June 27, 2025
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Understanding What It Is, How It Works, and Who Should Use It

When it comes to HIV prevention, PrEP (pre-exposure prophylaxis) is one of the most powerful tools available today. But how effective is it- really?

The short answer: When taken correctly, PrEP is over 99% effective at preventing HIV from sex and at least 74% effective from injection drug use.

In this article, we’ll explore:

What PrEP is and how it works
How effective it is in real-world situations
Who should consider taking it
Common myths and concerns
How to get started on PrEP
And answers to the most frequently asked questions

Let’s get into the details.

1. What Is PrEP?

PrEP stands for Pre-Exposure Prophylaxis. It’s a way for people who don’t have HIV but are at higher risk to prevent getting infected by taking a daily pill or occasional injection.

There are currently two main medications approved for PrEP:

Truvada® (emtricitabine/tenofovir disoproxil fumarate) – taken once daily
Descovy® (emtricitabine/tenofovir alafenamide) – also once daily, but not yet approved for people assigned female at birth
Apretude® (cabotegravir) – a long-acting injectable PrEP given every two months

These medicines stop HIV from taking hold in the body even if there is exposure.

2. How Effective Is PrEP at Preventing HIV?

PrEP is one of the most effective HIV prevention methods available- when used correctly.

✅ For Sexual Transmission:

PrEP reduces the risk of getting HIV from sex by 99% or more when taken daily
That includes vaginal sex, anal sex, and oral sex (although oral sex already carries a much lower risk)

✅ For People Who Inject Drugs:

PrEP reduces HIV risk by at least 74% when taken daily

These numbers are backed by real-world studies and global clinical trials involving thousands of participants.

Important: Missing doses can lower PrEP’s protection, especially for receptive anal sex. Daily use is strongly recommended.

3. How Does PrEP Work?

PrEP works by building up antiviral protection in your bloodstream and tissues. If HIV enters the body during sex or injection drug use, the medication blocks the virus from replicating and establishing infection.

Think of PrEP like a security guard that’s always on duty, stopping intruders (HIV) at the door.

💊 Oral PrEP (Truvada or Descovy):

Taken once per day
Can take 7–21 days to reach full protection:
- Anal sex: 7 days
- Vaginal sex/injection use: 21 days

💉 Injectable PrEP (Apretude):

Given as an injection every 2 months
Provides ongoing protection without the need to remember pills

4. Who Should Consider Taking PrEP?

PrEP is not for everyone- but it’s ideal for people at higher risk of HIV, including:

👤 Sexual Partners of People Living With HIV

Especially if their partner has a detectable viral load or is not on treatment.

👥 People Who Have Multiple Sexual Partners

Particularly if condoms are not used consistently.

🧑‍🤝‍🧑 Men Who Have Sex With Men (MSM)

MSM communities continue to be disproportionately affected by HIV.

👩‍⚕️ Transgender Women

Especially those who engage in unprotected sex or sex work.

🧪 People With Recent STIs

Having a recent STI increases HIV risk due to weakened mucosal barriers.

💉 People Who Inject Drugs

Especially if sharing needles or other injection equipment.

If you’re unsure whether PrEP is right for you, speak with a healthcare provider. There’s no shame in protecting your health.

5. Common Myths About PrEP (And the Truth)

Let’s clear up some misinformation:

❌ Myth 1: PrEP is only for gay men

Truth: PrEP is for anyone at risk– regardless of gender, orientation, or lifestyle.

❌ Myth 2: PrEP replaces condoms

Truth: PrEP prevents HIV- but not other STIs like gonorrhea, chlamydia, or syphilis. Condoms still matter.

❌ Myth 3: Taking PrEP means you’re promiscuous

Truth: Taking care of your health is never a sign of irresponsibility. It’s smart and proactive.

❌ Myth 4: You can take it only when needed

Truth: Daily use is essential for maximum protection- though “on-demand” PrEP (2-1-1 dosing) is an option for some men. Always consult a provider before using this method.

6. How to Start PrEP

Getting on PrEP is simpler than you think:

✅ Step 1: Talk to a healthcare provider

They’ll evaluate your risk level and explain your options.

✅ Step 2: Take an HIV test

You must be HIV-negative to start PrEP.

✅ Step 3: Get kidney function checked

Some PrEP medications can affect kidney health.

✅ Step 4: Choose your method

Discuss whether daily pills or injections work better for your lifestyle.

✅ Step 5: Stick with it

Stay consistent, attend follow-up visits every 3 months, and get tested regularly for HIV and STIs.

7. What Are the Side Effects of PrEP?

Most people tolerate PrEP well, but some may experience:

Short-term side effects (usually mild):

Nausea
Headache
Weight loss
Diarrhea

These often go away within the first few weeks.

Long-term side effects (rare):

Decreased kidney function
Reduced bone density

Your doctor will monitor these through regular checkups.

8. What If I Miss a Dose?

Missing a dose occasionally isn’t the end of the world- but consistency is key.

💊 For Daily Pills:

If you miss one pill, take it as soon as you remember
If it’s almost time for your next dose, skip the missed one
Try not to miss more than 2 days in a row

💉 For Injections:

Stay on schedule (every 2 months)
If you’re late, speak to your provider as soon as possible

Important: Missing too many doses can lower PrEP’s protection, especially for anal sex which requires a higher drug concentration.

9. PrEP and U=U: How They Work Together

If your partner is living with HIV and on ART, they may have an undetectable viral load, which means they cannot pass the virus on sexually (U=U = Undetectable = Untransmittable).

But if you: