PrEP: Everything you'd need to know

What is PrEP?

PrEP or Pre-Exposure Prophylaxis is a pill which when taken as directed can practically eliminate your risk of contracting HIV.

Who should take PrEP?

If you are HIV negative and at high risk of HIV then PrEP can stop your risk of contracting HIV. You might be considered at risk of contracting HIV if you:

  • Don’t always use condoms for anal or vaginal sex
  • Are an injecting drug user who doesn’t always use clean needles
  • Are a sex worker
  • Have a partner who is HIV positive with a detectable viral load or doesn’t take their HIV medication regularly
  • Have had a recent STI (especially a rectal infection or syphilis)
  • Use recreational drugs for chemsex (crystal meth, mephedrone and GHB)
  • Have recently needed PEP (Post-Exposure Prophylaxis)

If any of these factors apply to you, you will most likely be able to get PrEP for free on the NHS at any GUM clinic across Northern Ireland. To find out more click here.

Who shouldn’t take PrEP?

  • Your partner is HIV positive and ‘undetectable’ as this means their viral low is so low that they cannot transmit HIV onto anyone else by any means
  • If you’re always comfortable and confident to use condoms.
  • If you only engage in low risk sexual activities (oral, rimming, hand-jobs)

I’m not at high risk of HIV but would still like to take PrEP for peace of mind, is that possible?

Yes, it is! Whilst you may not be eligible to access PrEP on the NHS for free due to being at low risk of contracting HIV, you could still buy legal, genuine, generic-brand PrEP privately via for as little as £19 for a month supply (when you buy three months up front)

Are there side effects?

Generally, the vast majority of people taking PrEP do not experience any side effects. Just 1 in 10 people will experience mild nausea, diarrhoea, bloating or headaches but usually these side effects subside in the first month.

Occasionally, PrEP can reduce kidney function and/or bone health. This is why kidney tests are run before and during treatment as a precautionary measure.

How effective is PrEP?

PrEP is more than 99% effective at stopping HIV infection when taken correctly.

Things to do before you start PrEP

  • Get an HIV test

PrEP can only be used if you are HIV negative. If you are HIV positive and take PrEP you may cause drug resistance making your HIV more difficult to effectively treat. You can get a free self-test kit at or book a rapid HIV and syphilis test at The Rainbow Project. SH24 and GUM use fourth generation tests, meaning that these will tell you if you have HIV as long as you haven’t had any other risks of contracting HIV in the last four weeks. The Rainbow Project use third generation tests, these will tell you if you have HIV as long as you haven’t had any other risks in the past twelve weeks. It is advised to use condoms for anal or vaginal sex after you’ve completed your HIV tests and before you begin PrEP or to begin PrEP immediately after receiving your HIV negative results. Do not start PrEP if you have flu-like symptoms and had a recent HIV risk. Just in case these symptoms are related to you contracting HIV. If you’ve started PrEP and had a high risk encounter in the last four weeks, you should get another fourth generation test four weeks after beginning PrEP to be certain that an early infection was not missed.

  • Check your kidneys

Kidney tests involve a blood test for creatine and a urine test for protein. These tests should ideally be done before or on the day you start PrEP. If you are accessing PrEP privately you can still acess these tests at a GUM clinic for free. Just call any GUM clinic to book.

  • Test for Hepatitis B (HBV)

You can still use PrEP if you have HBV but it needs to be used more carefully. You can get tested for Hepatitis B via who will send you a free self-test kit if they feel you are at risk for HBV.

How do you take PrEP?

Daily PrEP: for giving/receiving anal & receiving vaginal or front hole sex

Taking PrEP every day is advisable for:

  • Receiving vaginal or front hole sex
  • Giving or receiving anal sex multiple times per week
  • Transgender and cisgender women who receive vaginal sex
  • Transgender men or non-binary people who receive vaginal or ‘front hole’ sex
  • Anyone who may benefit from having an easier dosing routine
  • Anyone who may occasionally accidentally miss a dose
  • Those who have Hepatitis B

In all these cases its best to take PrEP for at least seven days before beginning to have unprotected sex to allow the medication to reach protective levels needed. If you know you’re going to be at risk of HIV within the next few days of beginning PrEP you may want to start with a double dose.

On-Demand/Event-Based Dosing

On-Demand or Event-Based Dosing is only a viable option for those who are giving/receiving anal sex or giving vaginal sex. Especially if you are only having sex once per week or having sex several times over a few days per week. This type of dosing will not work for people receiving vaginal sex.

On demand dosing involves:

  1. Taking a double dose of PrEP (two pills) before you have sex. Ideally this should be done between 2 and 24 hours beforehand.
  2. Taking a single pill 24 hours after the double dose
  3. Taking another single pill the following day, 24 hours later

Although the pre dose is important for the highest protection, if you miss or are late with the pre dose, taking the double dose as soon as possible will still give some protection.

 Routine Care for when you’ve started PrEP

Every 3-4 months

  • Have a 4th generation HIV test
  • Have a full STI test
  • If you are over forty years old or are at risk of kidney problems, a blood test for kidney function

Every 12 months

  • Have a blood test to check your kidney function
  • Test for hepatitis C, if you are having sex with gay or bisexual men.

What to do if you miss a pill?

If you miss one or two pills occasionally, this will be fine on a daily dosing regime.

If you are daily dosing and miss more than a week of pills you will need to wait until you’ve had at least seven daily doses of PrEP or take a two-pill dose before you are completely protected from contracting HIV again.

Can I stop PrEP completely?

You can stop taking PrEP whenever you feel it is no longer necessary for you. However, remember to continue taking PrEP daily for seven days if you’ve recently had receptive vaginal sex or continue taking PrEP daily for two days if you’ve recently given or received anal sex.

If in the future your circumstances change again, it is easy to restart PrEP.

 How do I get PrEP on the NHS?

You will need to call your local GUM clinic as you normally would when you’re booking a full STI test but instead ask for a ‘PrEP assessment’ 

For more details on whether you’re eligible to get PrEP on the NHS and contact details for all GUM clinics in Northern Ireland click here

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