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What is PrEP on‑demand?

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PrEP on-demand 101

PrEP on-demand can be an effective HIV prevention option for those with infrequent, planned sexual habits.

PrEP on-demand (PrOD), like daily PrEP, requires a prescription from an approved PrEP provider in Canada. It’s less frequently prescribed because PrOD requires more planning than daily PrEP.

If taken correctly, PrEP on-demand can offer up to 99% protection against HIV during anal sex.

Patients must start the PrEP on-demand regimen 2-24 hours before a planned sexual encounter.

Only Truvada and its generic form can be used for PrEP on-demand. Descovy cannot be prescribed as PrEP on-demand.

PrEP on-demand 101

PrEP on-demand can be an effective HIV prevention option for those with infrequent, planned sexual habits.

PrEP on-demand (PrOD), like daily PrEP, requires a prescription from an approved PrEP provider in Canada. It’s less frequently prescribed because PrOD requires more planning than daily PrEP.

If taken correctly, PrEP on-demand can offer up to 99% protection against HIV during anal sex.

Patients must start the PrEP on-demand regimen 2-24 hours before a planned sexual encounter.

Only Truvada and its generic form can be used for PrEP on-demand. Descovy cannot be prescribed as PrEP on-demand.

What is PrEP on‑demand?

PrEP is an acronym for Pre-Exposure Prophylaxis, a daily pill that helps prevent people from contracting HIV when taken correctly.

There are two ways PrEP can be prescribed to be taken:

How to take PrEP on‑demand: The 2‑1‑1 method

PrEP on-demand has only been shown to work with the Truvada version of PrEP and its generic forms. Descovy, the newest form of PrEP, has not been approved to use as PrEP on-demand.

PrEP on-demand is often referred to as the 2-1-1 regimen. It consists of a total of 4 pills taken in the following order:

Pills #1-2

Two to twenty-four hours before sexual contact

Pills #3

Twenty-four hours after pills #1-2

Pills #4

Twenty-four hours after pill #3

PrEP on-demand has only been shown to work with the Truvada version of PrEP and its generic forms. Descovy, the newest form of PrEP, has not been approved to use as PrEP on-demand.

PrEP on-demand is often referred to as the 2-1-1 regimen. It consists of a total of 4 pills taken in the following order:

THURS

9:00 AM

Take PrEP
pills #1-2

THURS

11:00 PM

Has sex

FRI

9:00 AM

Take PrEP
pill #3

SAT

9:00 AM

Take PrEP
pill #4.

They’ve now completed their PrEP on-demand.

Transitioning from PrEP on‑demand to daily PrEP

Once you complete the PrEP on-demand routine (ex: Saturday), you have the option to maintain protection by continuing to take PrEP at the same time every day; this is known as daily PrEP.

What if the same person from our previous example wants to have sex on Saturday as well?

The most important thing is that they take PrEP twice before sex and for two days afterwards. Here’s how the updated timeline would work:

THURS

9:00 AM

Take PrEP pills #1-2

THURS

11:00 PM

Has sex

FRI

9:00 AM

Take PrEP pill #3

SAT

9:00 AM

Take PrEP pill #4

SAT

10:00 PM

Has sex

SUN

9:00 AM

Take PrEP pill #5

MON

9:00 AM

Take PrEP pill #6. They’ve now completed their PrEP on-demand and can begin daily PrEP.

This person can continue taking a single PrEP pill daily for maximum protection (99%), which is known as daily PrEP. If you want to stop taking PrEP or take a break and start it again later, be sure to take your daily tablet for at least two days after your last sexual encounter.

Who should take PrEP on-demand?

PrEP on-demand has only been approved to prevent HIV transmission through anal sex - those having vaginal/frontal sex should not consider PrEP on-demand due to differences in the time it takes PrEP to act in body tissues. PrEP on-demand has not been studied for HIV transmission through injection drug use and should not be used for persons with this risk behaviour.

PrEP on-demand can only be taken by patients that are HIV-negative and prescribed to take PrEP this way by their clinician. Whenever possible, prescribing daily PrEP is preferred as this offers the highest rate of HIV protection.

However, PrEP on-demand is still considered to be effective at HIV prevention and is more likely to be a fit for those that:

Have less financial ability to pay for daily PrEP

Don’t have access to housing or the storage of medication

Struggle with daily adherence

Have anal sex infrequently and plan their encounters in advance

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How effective is PrEP on-demand?

PrEP on-demand offers 99% efficiency

Daily PrEP offers 99% efficiency

Recent studies show that PrEP on-demand is an effective tool for HIV prevention and is equally effective to daily PrEP when taken properly.

If you take PrEP on-demand, it’s important to adhere to the prescribed dosing guidelines by taking it 100% of the time for all sexual encounters. This is because taking PrEP less frequently decreases the drug’s protective effects against HIV.

When taken correctly, PrEP on-demand has an overall efficiency of 99% in preventing HIV among men who have sex with men.

Are there any side effects from PrEP on-demand?

LESS THAN 10% OF PATIENTS EXPERIENCE SIDE EFFECTS FROM PrEP ON DEMAND.

The most common side effects are nausea and diarrhea. These symptoms might be mild or severe. Other possible side effects include headaches, dizziness, and abdominal pain or cramps (in the stomach).

Although these are experienced more frequently among PrEP on demand than daily PrEP medicine users, the amount of patients that experience side effects is still generally low.

PrEP on-demand vs. daily PrEP

PrEP On‑Demand

Daily PrEP

Approved PrEP Medications

Truvada, Generic Truvada

Truvada, Generic Truvada, Descovy

Rate of Protection

99% for anal sex
*Not approved for vaginal sex or drug injection

99% for anal/vaginal sex
84% for drug injection

How long until it's effective?

Anal sex: 2 hours

Anal sex: 7 days
Vaginal sex: 21 days
Drug injection: 7 days

Is PrEP on-demand right for me?

Whether you choose to take PrEP on-demand or daily is your choice. It’s important to understand that most providers in Canada will prescribe daily PrEP when possible, as it’s more effective in preventing HIV and more regulated.

However, if you are considering on-demand PrEP and think it would better suit your current situation, feel free to chat with your PrEP provider. They should be able to advise you on the best dosing schedule and how to best continue preventing HIV in a way that works for you.

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FAQs

Is PrEP on demand as effective as daily?
Does PrEP work after 1 hour?
Can Truvada be used on-demand?
Should I take PrEP on-demand in the morning or at night?

Reviewed by:

Dr. Caley Shukalek

Caley is passionate about evidence-based patient-centred care, including telemedicine that can provide high quality care from wherever a patient may choose.

He helped create Alberta’s PrEP guidelines and works as a specialist in General Internal Medicine with additional training in sexual health, including HIV and sexually transmitted infections.

He holds a Masters of Public Health from Johns Hopkins University, an MD from the University of Calgary and an MSc from the University of Alberta.