Health Hub
Sexual wellness
What Is PrEP on Demand?

What Is PrEP on Demand?

Updated on:
January 18, 2022

What Is PrEP on Demand?

What is PrEP? PrEP is an acronym for Pre-Exposure Prophylaxis, a daily pill that helps prevent people from contracting HIV when taken correctly. This method of protection currently comes in three types of approved pills (Truvada, generic Truvada, & Descovy medication). All of which offer a similar level of protection when taken daily (99%). PrEP on-demand is a breakthrough in HIV prevention, so far it has only been approved and studied among people who are having anal sex and/or men who have sex with men. 

Where daily PrEP requires once a day dosage, PrEP on-demand does not require daily intake. This is ideal for someone who can’t access a sufficient supply of PrEP, has fluctuating sexual behaviour, or is forgetful. Some refer to these types of PrEP regimen as on-demand, intermittent use, non-daily doses, and off-label prescription.

How Does PrEP On-Demand Work?

What does the dosing for on-demand PrEP look like? To take PrEP on-demand, most use a 2-1-1 dosing schedule, which includes:

  • Taking two PrEP pills 2 to 24 hours before sexual contact, and
  • Taking one pill/day, for two days. Starting 24 hours after your step 1 dose (total of 2 pills, one pill/day)

How Effective Is PrEP on Demand?

If you take PrEP on-demand, it's important to adhere to the prescribed dosing guidelines. This is because taking PrEP less frequently decreases the drug's protective effects against HIV. 

When taken as described, PrEP on-demand has an overall efficiency of 86% in preventing HIV among men who have sex with men

Are There Any Side Effects from PrEP on Demand?

A few 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.

If you are worried about side effects, you may want to consider Descovy for PrEP, which has a slightly lower report of side effects.

Should I Take PrEP On-Demand or Daily?

Whether you choose to take PrEP on-demand or daily is your choice. It’s important to understand that most providers in Canada will choose to prescribe daily PrEP 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 have a chat with your PrEP provider. They should be able to best advise you on best dosing schedule and how to best continue preventing HIV in a way that works for you.

Where Do I Get PrEP?

  1. Consult with your clinician: A clinical visit will help you decide if PrEP is ideal for you or not. They ask about your sexual activity, drug use and other behaviours that can increase your risk of HIV. 
  2. Lab Tests: These tests are for HIV status, sexually transmitted infections, and kidney function to determine if your body can handle PrEP. If results are satisfactory, you may have a 30-day prescription. 
  3. Repeat Lab Tests: Go for a lab test after one month, then repeat every three months. This is necessary to detect and treat any STIs and also ensure that you remain HIV negative.


For HIV-negative patients having anal sex, PrEP on-demand can be a good way to take preventive action and stay safe. Remember that it is not 100% effective but does provide an additional layer of protection.


Reviewed by:
Thomas Trombetta

Thomas is passionate about gender and sexuality liberation social movements. Before beginning his work with Freddie, Thomas studied Sociology and Global & Development Studies at the University of Alberta, after which he began working with marginalized communities. In previous roles, Thomas was involved in queer and trans health education, PrEP health promotion, community-based research, HIV education, and LGBTQ2S+ advocacy.