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What is PrEP?

Pre-Exposure Prophylaxis (PrEP) is an antiretroviral medication used to reduce the risk of getting HIV.

PrEP, when taken regularly as prescribed, can reduce your risk of getting HIV by up to almost 100%.

Who can take PrEP?

PrEP can be taken by anyone who is HIV-negative and at a medium to high risk of getting HIV. Factors related to a higher risk of HIV include:

  • Being a gay or bi-identifying person
  • Having a recent STI (especially rectal infection or syphilis)
  • Using recreational drugs
  • If your partner is HIV-positive and finds it hard to stay on their meds

How do I get PrEP?

If you want to start taking PrEP you will need to get a script from your doctor or GP. M Clinic has GPs that are experienced with prescribing PrEP, while the WA Department of Health also provides a list of trained PrEP prescribers.

You will need to have a few tests taken at your initial consultation, including a blood test, kidney function test, and a full sexual health screening.

It’s important that you have an HIV test before you start taking PrEP because it only works if you don’t have HIV. If you already have HIV and don’t know it, you could develop drug resistance as PrEP by itself is not adequate treatment for HIV.

In rare cases, PrEP can reduce kidney function, so a kidney function test is used to track your baseline kidney function.

If you have hepatitis B (HBV) you can still take PrEP, but it needs to be used more carefully. You will need to take PrEP every day and need to talk to your doctor if you want to stop PrEP.

How do I take PrEP?

There are a few different ways to take PrEP. Most PrEP studies looked at PrEP taken daily, which is the recommended way of taking it. On-demand PrEP is another option, though less effective.

Talk to your doctor about which is the right option for you, and follow your doctor’s advice about how to take PrEP effectively.

Taking PrEP daily

Daily PrEP

If you have sex regularly or want consistent HIV protection, taking PrEP daily is the best option.

Daily PrEP involves taking one pill a day, every day. It keeps sufficient levels of the drug in your body 24/7. You can have sex when you want and involves less need for planning.

If you miss a dose, daily PrEP still provides a high level of protection, though you want to avoid missing doses as much as possible. It’s a good idea to find a routine that works for you so you can take your pills at the same time every day. Consider using things like calendars or tracking apps on your phone to make sure you remember to take your pill.

Taking PrEP on demand

On-Demand / Event Based PrEP

On-demand PrEP, also called event-based or 2-1-1 PrEP, is another option. It involves taking a specific sequence of PrEP around the times you are having sex and requires planning in advance. It is less effective than daily PrEP (94% vs 99%). On-demand PrEP can only be used for cisgender men having anal sex, due to lack of evidence in other populations.

Here are the steps to on-demand PrEP:

  1. Take two pills between 2 – 24 hours before you have sex
  2. Take one pill 24 hours after the double dose
  3. Take one pill 48 hours after the double dose
  4. If you have repeated sexual activity, take one pill every day until 48 hours have passed since you last had sex.

Do I need to keep using condoms?

While PrEP works at preventing HIV, it does nothing to stop STIs like chlamydia, gonorrhoea, syphilis and herpes.

Condoms are the best way to prevent HIV, STIs and pregnancy, and you can get them for free from all our services and all over the place.

If you don’t know your size, you can also order WAAC’s Find Your Right Fit pack of different sized condoms.

Studies show that anxiety around sex is significantly reduced for people who use both condoms and PrEP, which can help make sex more fun and pleasurable!

I’ve started PrEP! What next? What do I have to keep doing?

Once you start PrEP, monitoring is just as important. You need to have a check-up one month after commencing PrEP to make sure your kidneys are coping with the medication and to have a repeat HIV test.

Following this, you should have a check-up every three months, no matter what type of dosing regimen you use. If you are currently using PrEP and have not been monitored, talk to your doctors about doing this now.

Remember, PrEP only works to prevent HIV so if you are sexually active and want to prevent STIs like syphilis, chlamydia and gonorrhoea, using condoms is the best way.

Frequently Asked Questions

Are there side effects? I’ve heard there are side effects!

The majority of people taking PrEP do not get side effects.

However, like all medicines, PrEP has the potential to cause side effects. In studies, mild nausea, diarrhoea, bloating and headache were reported in the first month by less than 1 in 10 people. These side effects then usually stop within the first month or so.

Occasionally, PrEP can cause more serious side effects that reduce kidney function and/or bone health. For this reason, regular check-ups and monitoring kidney function is part of your doctor’s procedure to get a script for PrEP.

Is there anyone who should not take PrEP?

PrEP should NOT be used by people who are HIV positive.
PrEP is usually not needed if:

  • The negative person only has HIV positive partners who are on ART with undetectable viral load. An undetectable viral load means that an HIV positive person is not infectious.
  • If you are happy and able to always use condoms.
  • If you are in a monogamous relationship and both you and your partner have tested HIV negative.
How much does PrEP cost?

Once you have a PrEP prescription, you can go to the pharmacy and get your PrEP just like any other medication. PrEP is listed on the Pharmaceutical Benefits Scheme (PBS), which keeps the cost low for people with a Medicare card. It gets cheaper for people with concessions.

If you are Medicare ineligible and unable to get PBS listed medication, it can be expensive to buy at a pharmacy. Many people choose to personally import their PrEP from overseas as a safe and affordable option. See the table for more information.

Description Cost Link
Australian Pharmacy (PBS) Requires a prescription. Purchase PrEP at a local pharmacy (requires Medicare) $30/month ($6.60/month with concession) PrEP on the PBS
Personal Importation (for people without Medicare). Requires a prescription. Import generic medication from overseas pharmacies via Personal Importation Scheme. See links for more information. PrEP access now (PAN)
PrEP Global
What do I do if I miss a pill?

Missing one dose is unlikely to cause any problems. If you miss one, this will be fine. Don’t stop PrEP, just carry on once you remember. Drug levels will still be high enough to protect against HIV.
If you are missing several doses each week, please talk to your clinician about support.

If you use daily dosing and miss more than a week of pills, then restart with a double dose (two pills) and then continue with one pill a day. Never take more than one double dose when you start PrEP. You only need one double dose at the start. More than one double dose in a week may be harmful. Do not take more than a total of seven pills in one week.

  • Pick a regular time and try to stick to this each day. Link it to a routine task like brushing your teeth. It doesn’t have to be the exact same time but it will help get you into a routine.
  • If you have a break from PrEP and have risks during this time, it is important to have another HIV test.
How do I stop taking PrEP?

Stopping PrEP is OK as long as it is done safely.

If you want to stop taking PrEP altogether, it is recommended you continue to take it for 28 days after your last potential risk. That is because if you have been exposed to HIV during that risk event the medication continues to protect you until the virus is dealt with.

If you’re a cisgender man who has sex with men, the current recommendations say you only need to take PrEP for two days after your last risk event and then you can stop.

It’s wise to discuss your decision to stop with your doctor. You might want to discuss plans to stop PrEP with your partner(s) and get tested for HIV and other infections together.

If in the future your circumstances change again, it is easy to restart PrEP. If you stop PrEP and have a risk afterwards, contact your clinic in case post-exposure prophylaxis (PEP) might be needed. In the cases when PEP is used, it needs to be started as soon as possible.

How does PrEP work?

PrEP works by blocking HIV’s ability to replicate. HIV needs to enter CD4 cells (a type of immune cell) for it to be able to reproduce and spread.

PrEP creates a wall around CD4 cells, blocking off the receptors into the cell. This means that HIV can enter the body but won’t be able to replicate itself and won’t be able to spread throughout the body.

Essentially, PrEP is the bouncer at a club, keeping out people who are intoxicated and aggressive and maintaining a safe and enjoyable space to party.

How long does it take for PrEP to work?

There needs to be sufficient levels of the drug in your body for it to protect you from HIV. For most people, it takes 7 days of daily dosage for it to reach the optimal levels you need for protection.

If you are a cisgender man, taking two pills at least 2-24 hours prior to sex (on demand PrEP) will provide protection against HIV.  If you are a trans man, cis woman, or were assigned female at birth, it can take up to 21 days for it to become effective.

I’m trans. Can I still take PrEP?


PrEP is beneficial for anyone who wants to reduce their risk of HIV, including trans and gender diverse people. PrEP has not been shown to affect your levels of transition-related hormones (testosterone, oestrogen, etc.) but it is recommended that you take PrEP daily. Currently there is not enough data to support on-demand use for transmen and transwomen.

Talk with your doctor about PrEP and hormones for further support.

I’m HIV positive. Can I take PrEP?

Nope. PrEP is only useful at preventing HIV infection for HIV-negative people.
While the drugs in PrEP are used to treat HIV for some people, they are in higher concentrations, and PrEP will not effectively treat your HIV. In fact, taking PrEP if you are HIV-positive can result in drug resistance.

Your doctor will be able to prescribe medication that works best for treating you.
Taking your antiretroviral medication as prescribed and lowering your viral load to undetectable levels means you cannot transmit HIV to others through sex. This is referred to as Undetectable = Untransmittable or U=U.

I have hep B. Can I still take PrEP?

If you have hepatitis B, it is important that you take your PrEP every day. The drugs in PrEP are also used as part of the treatment for hepatitis B. This means missing doses can have implications for your treatment and potentially impact your liver.

Make sure you talk with your doctor about your hepatitis B treatment and taking PrEP so they can manage your care in the best way possible.

What is in PrEP?

PrEP is a two-drug antiretroviral medication containing emtricitabine and tenofovir disoproxil fumarate.

Truvada is the main brand name but it is also available in generic, non-branded versions.

Does PrEP interact with other medicines?

PrEP does not interact with most other medicines. But if you are prescribed other meds, always tell your doctor (including your GP) that you are taking PrEP. You can also ask a pharmacist to check for drug interactions, including with over-the-counter meds.

One important exception is that tenofovir (TDF) does interact with some non-steroidal anti-inflammatory drugs (NSAIDs), especially diclofenac. Taking both drugs together can cause kidney problems. Other NSAIDs include ibuprofen and naproxen. Avoid using these meds if you are taking PrEP, or let your doctor know if you need to take them.

Info on interactions between PrEP and other meds, including hormone treatment is on this site from Liverpool University. There is also a free app that is downloadable on most phones – search for ‘Liverpool HIV iChart’.

Can taking PrEP lead to HIV resistance?

If you take PrEP correctly, the chance of drug resistance is very low.
Firstly, resistance relates to HIV and not the person. So an HIV negative person can’t be resistant. Secondly, resistance is only a risk if you become HIV positive. Even then the risk is low.

The risks of drug resistance are from:

  • Starting PrEP without knowing that you are already HIV positive. This is why the HIV test before PrEP is essential.
  • Becoming HIV positive during a break from PrEP and then not having an HIV test before restarting.
  • Missing too many PrEP doses, so that drug levels are too low to prevent HIV infection.
  • Contact with drug-resistant HIV. This is very rare: globally, only two cases have been reported of PrEP not working because of drug-resistant HIV
How do I know if someone is taking PrEP?

There is no way to know if someone you are having sex with is really on PrEP (or taking it correctly).

Only you can be sure if you are using PrEP to prevent HIV. If you are worried about the risk, you can use condoms and lube for additional protection.

More information


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