How Effective is PrEP for Preventing HIV Infection?

by | Sep 23, 2023 | LGBTQI+ Health, Sexual Health | 0 comments

Pre-exposure prophylaxis (PrEP) does an excellent job of protecting you from HIV infection.

The oral medication is up to 99% effective when taken as prescribed.


HIV-negative people who have a high risk of HIV exposure are the primary users of PrEP. Those in high-risk groups include men who have sex with men, transgender women, and injecting drug users.

It’s also available to anyone who feels at risk of acquiring HIV.

What is PrEP?

PrEP is a combination of two medications, tenofovir plus emtricitabine, that comes in a single, once-a-day tablet.

Truvada was previously the most commonly dispensed brand of tenofovir/emtricitabine but is no longer funded by the Pharmaceutical Benefits Scheme (PBS).

Not being on the PBS has made Truvada prohibitively expensive.

Pharmacies now dispense generic versions of PrEP (containing the two medications) that are on the PBS, making them much cheaper.

The Therapeutic Goods Administration has approved all generic versions of PrEP which are just as effective as Truvada.

PrEP shouldn’t be confused with post-exposure prophylaxis (PEP). As the name suggests, PEP is typically taken by HIV-negative people after being exposed to the virus.

The aim here is to reduce the chance of HIV taking hold.

Have a look at for more information on PEP.

How PrEP Works

PrEP works by blocking an enzyme called HIV-1 reverse transcriptase (HIV-1 RT). This enzyme is responsible for replicating the most common form of HIV as it grows unabated inside the body.

There needs to be enough PrEP in your system to effectively block HIV-1 RT, which is why you need to take the medication as directed consistently.

PrEP can either be taken daily, on-demand or periodically.

Daily PrEP is precisely that – a pill you take around the same time each day for as long as you’re sexually active and need protection.

Taking PrEP daily is considered the most effective method. If casual or spontaneous sex is your thing, then daily PrEP will provide you with protection 24/7.

On-demand PrEP suits those who can plan for sex ahead of time, don’t want to take a pill every day, or have other health conditions that the medication might impact.

With this method, you take two pills 2-24 hours before and after you have sex, followed by two more pills over the next 48 hours.

It’s best to talk with your GP about the pros and cons of this option.

Periodic PrEP is when you take a pill a day over a period when you expect your sexual activity to increase. Such periods may include during festival season or when a special friend is in town.

Periodic PrEP is a popular method for people worried about side effects. It’s also a good option for which to begin taking the medication.

Again, please speak with your GP about dosages and timings as they relate to your circumstances.

Are There Any Side Effects of PrEP?

As with most medications, some side effects come with taking PrEP – though we deem these relatively low risk.

blue prep pill in hand

The vast majority of people don’t experience any problems whatsoever. However, some short-term effects may include:

  • an upset stomach;
  • diarrhoea;
  • weight loss;
  • mild headaches, and
  • loss of appetite.

In rare cases, if taken over a long period of time, PrEP can decrease kidney function in those with pre-existing medical conditions.

To be safe, most GPs recommend PrEP users get regular kidney tests.

Taking a different perspective, there can also be positive side effects of PrEP, namely improved mental health. For some people, the fear of acquiring HIV interferes with their ability to relax and enjoy sex.

PrEP can be an extra layer of protection in addition to condoms, so people know they’re as safe as possible.

An excellent article related to this topic is Sex Without Fear by journalist and novelist Tim Murphy.

What are Some Other Ways to Safeguard Against HIV Infection?

Whether you’re taking PrEP or not, practising other techniques to protect against HIV infection is a great idea.

close up green condom

Though I’m sure everyone is well aware of the many prevention options, I wouldn’t be doing my job without urging you to:

  • Use condoms when having sex.
  • NEVER share needles – even with someone you love and trust.
  • Get tested regularly.
  • Educate yourself on how and when to take post-exposure prophylaxis (PEP).

It’s also essential to understand that PrEP doesn’t protect you against any other sexually transmitted infections (STI).

How to Get Started With PrEP

Starting on PrEP is as easy as visiting your doctor or sexual health practitioner for a discreet, non-judgemental chat.

I’ll ask you a bunch of questions about your sexual activity to help determine your risk of HIV exposure.

I’ll then order a blood test to confirm that you’re HIV-negative. At the same time, I’ll test you for hepatitis B, kidney health, and other STIs.

After you get the all-clear, it’s just a matter of answering your questions before sending you on your way, prescription in hand.

Once you start taking PrEP, you’ll need to see your GP every three months for a sexual health check and repeat prescription if need be.

Like More Information?

For those who’d like to dig a bit deeper, there’s loads of information available on PrEP and related topics:

Dr Sophie Carter blog

Dr Sophie Carter is a local GP at Doctors of South Melbourne.

She has special interests in men’s health, women’s health, and sexual health.

You can make an appointment online with Sophie or call us on 8579 6838.


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