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Pre-Exposure Prophylaxis (PrEP)

Pre-Exposure Prophylaxis (PrEP) is offered when a person is at very high risk of acquiring HIV infection.
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Pre-Exposure Prophylaxis (PrEP)

Pre-Exposure Prophylaxis (PrEP) is offered when a person is at very high risk of acquiring HIV infection. PrEP is advised to be taken daily to lower a person’s risk of getting HIV infection. When PrEP is taken daily, studies have shown it has effectively reduced the risk of getting HIV about 99% from sex and at least 74% from injection drug usage.

If taken daily, PrEP is very effective in preventing an HIV-negative person from getting HIV from sex or injection drug user partners who are HIV-positive. PrEP is less effective when the medication is not taken compliantly.

Currently, the only FDA approved PrEP is a combination of two HIV medication.

How does PrEP work? Does it work the same way as vaccine?

PrEP works differently from vaccine. Vaccine helps your body fights off infection by building antibodies. PrEP are made up of pills that are taken daily by mouth. The presence of the medicine in your body can help stop HIV from occurring and spreading in your body. However, if you do not take PrEP every day, there may be insufficient medicine to block off the virus.
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Should I consider taking PrEP?

PrEP may be useful for you if you are HIV-negative and the following applies to you:

You are heterosexual and you:

  • Have a partner who is HIV positive
  • Have multiple partners, a partner who has multiple partners, a partner with unknown HIV status and you have increased risks of HIV infection such as:
    • You don’t use condoms having sex with people who inject drugs
    • You don’t use condoms having sex with bisexual men

You are a gay/ bisexual man and you:

  • Have a partner who is HIV positive
  • Have multiple partners, a partner who has multiple partners, a partner with unknown HIV status and you:
    • Have anal sex without condom or
    • Recently had another STIs

You are a drug user and you:

  • Share equipment and needles with others to inject drugs
  • Are at risk of getting HIV from sex

If you have a partner who is known to be HIV-positive and are considering pregnancy, PrEP may be an option to protect you and your baby from acquiring HIV infection when you are trying to conceive, during pregnancy and during breastfeeding period.

Don’t hesitate to speak to your doctor.

How well does PrEP work?

PrEP is very effective if taken correctly and taken daily. When PrEP is taken daily, studies have shown it can reduce the risk of getting HIV about 99% from sex and at least 74% risk reduction from injection drug users.

PrEP does not protect against other STIs, you are advised for responsible safe sex and use of barrier contraception every time when you have sex.

Is PrEP safe? Any other Side effects?

PrEP does not cause any serious life-threatening side effects. Common side effects include nausea in certain people, but the symptoms improved over time with repeat consumption of the medication.

Currently, there are no significant negative health side effects reported for people who are HIV-negative and taking PrEP for up to 5 years.

What do I expect when I see my doctor?

You will need regular visits and follow up with your doctor when you are on PrEP. Your doctor will offer you baseline blood tests to check your kidney and liver blood tests function and a baseline HIV test before starting you on PrEP. You may be offered blood tests including HIV tests 3 monthly when you are on PrEP.

How to take PrEP?

There are few ways for taking PrEP, please consult your doctor, as this can be tailored to your individual lifestyle.

Daily PrEP Routine
PrEP is advised to be taken at the same time every day. A few hours earlier or late is okay. If you miss a pill from time to time, you are likely to still have sufficient protection.

Daily PrEP is suitable for anal and vaginal sex. The lead-in time for daily PrEP is 7 days.

On-Demand PrEP or Event-Based Dosing PrEP

  • If you anticipate a condomless sex on a particular date/time:
    • Take 2 pills 2-24 hours before sex,
    • Take 1 pill on the day of sex, and
    • Take further 1 pill 24 hours after sex.
    • If you have sex for an extended time frame over days, you can continue to take the pill daily until you have 2 sex-free days.
  • You should not miss any doses.
  • On Demand PrEP is not suitable for people with hepatitis B infection, as this option can cause a flare-up of the virus leading to inflammation of the liver.

On-Demand PrEP is as effective as daily PrEP for anal sex, there is lack of studies on its efficacies on vaginal sex.

The Ts and Ss- 4 pills per week regimen

  • You are advised
    • daily dosing for 7 days (leap-in time), then
    • drop the pills to 4 pills per week. As the name suggested, you can choose to take the pill on Tuesday, Thursday, Saturday, and Sunday.
  • This option is suited to people with sex lifestyle of 1-2x month and people who are not keen to take daily pills. Some people who are on On-Demand PrEP regimen may notice they have just been taking 4 pills per week for most time can opt for this option instead.

The Ts and Ss are suitable for anal sex, there is a lack of studies on its efficacies on vaginal sex.

Holiday PrEP

  • Holiday PrEP is based on a 7-day period, known as 7-7-7:
    • daily dosing for 7 days prior to the period of sex, followed by
    • 7 days of daily dosing during the period of sex (or as long as the specific sex period lasts), and
    • another 7 days of daily dosing after sex.
  • Holiday PrEP is suited for a pre-planned period of time when you know your risk of exposure to HIV can be higher in situations such as
    • Having sex when abroad in a place with a high prevalence of HIV
    • Where alcohol or drugs substances may be used
    • Condoms are not used
    • Increased number of sexual partners with unknown HIV status

Holiday PrEP is suitable for both anal and vaginal sex.


You should take PrEP as advised by your doctor. However, your doctor may advised you to stop taking PrEP in situations such as:

  • A change of lifestyle that lowers your risk of getting HIV infection
  • Poor compliance; you may forget or not keen to take the pill daily, and have other better and suitable ways of protecting yourself from HIV
  • You experience side effect from the medicine, affecting your daily life, experience abnormal blood tests due to reaction from PrEP


  • In receptive anal sex, if PrEP is taken every day, it reaches its maximum protection against HIV at 7 days of daily consumption.
  • In receptive vaginal sex and injection drug use, if PrEP is taken every day, it reaches its maximum protection against HIV at 20 days of daily consumption.
  • At this moment, there are no statistics to show the duration for PrEP to be maximally effective for insertive anal or vaginal sex.


You should not stop using condoms. PrEP does not protect you against other STIs. While PrEP does significantly reduce your risk of acquiring HIV infection when taken daily, condoms give extra protection especially to patients who have issues taking PrEP.

Can I start taking PrEP after I have been exposed to HIV?

PrEP is only suited for people with constant ongoing high risk of acquiring HIV infection. If you are recently exposed to HIV during sex or through needles or works preparing drugs, you should consider PEP (Post-Exposure Prophylaxis). PEP should be considered as soon as possible after exposure to potential HIV infection. PEP can be given within 72 hours of possible exposure to HIV. Do discuss further with your doctor on PEP.

Be safe, it’s not just about sex, it’s about your health, not just your heart.

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