The 2-1-1: Understanding PrEP On-Demand for HIV Prevention


PrEP is one of the most effective HIV prevention methods available when the medication is taken as prescribed. Typically, PrEP medication must be taken daily for a minimum of seven days before it is fully effective for receptive anal sex. It must be taken for 21 days to be effective for protection for receptive vaginal sex or injection drug use.

While PrEP can be up to 99% effective when taken daily, many people have trouble staying on schedule with their regimen. Missing a dose of PrEP or not taking the medication for several days in a row can increase the chances of HIV transmission and lower the drug’s effectiveness.

Further, PrEP can be quite expensive if it is not covered under insurance. The cost of HIV treatment can be lowered through some payment plan options and discount services, but it can deter some people who are at a high risk of HIV transmission from getting PrEP.

Thankfully, there is another method known as On-Demand PrEP – or the 2-1-1 – which is proven to be equally as effective as a daily regimen when taken correctly.

What is PrEP On-Demand?


PrEP On-Demand is also known as PrEP 2-1-1 or event-driven PrEP. Rather than taking the medication once a day for a set amount of time, a person who is at risk of HIV transmission can take two pills anywhere between 2 to 24 hours before a sexual encounter and one pill 24 hours and 48 hours later. Hence, why it is sometimes called PrEP 2-1-1.

According to a recent study published in Clinical Infections Diseases, a study followed 279 male patients who used PrEP On-Demand for a total of 3 months. After a one year follow up, there were no new cases of HIV transmission from any patients who used the 2-1-1 regimen.

Currently, only the PrEP drug Truvada has been studied for on-demand HIV prevention regimen. Descovy has not yet been approved for event-based PrEP.

What are the Pros and Cons?


One of the greatest benefits to using the PrEP On-Demand regimens is that it eliminates the need to take HIV prevention medication every single day. This offers more flexibility and can provide the same amount of protection if taken as directed by a doctor.

This can also be helpful for people who cannot afford medication, do not have health insurance, or do not qualify for discounted payment options. Rather than having to purchase monthly refills, the prescription can be taken and refilled as needed.

Currently, doctors agree that it is a viable HIV prevention strategy for male patients who participate in infrequent sex with partners who are either living with HIV or whose HIV status is unknown. It has been determined to be equally effective for both male tops and bottoms.

There are seemingly very few downsides to PrEP On-Demand. According to the study, only 14% of patients who participated in the study following the 2-1-1 PrEP method described any challenges with the regimen. These reported issues included:

  • Not planning far enough in advance
  • Forgetting to take the following doses
  • Experiencing side effects from PrEP

Do You Qualify?


Currently, PrEP On-Demand has only been studied on cis-gender males participating in receptive or insertive anal sex. It has not been studied for HIV prevention in women, transgender women, or transgender men.

One of the reasons why On-Demand PrEP is not approved for women is due to the fact that PrEP is more effective in less time in rectal tissues – compared to vaginal tissues. There are currently no studies underway for the use of PrEP in other genders.

PrEP On-Demand can only be used for protection from HIV transmission through sexual contact. It has not been studied as an HIV prevention method for unsafe injection practices.

Therefore, in order to qualify for PrEP On-Demand, you must:

  • Be a cisgender male who participates in sex with other men
  • Require HIV prevention medication infrequently
  • Would benefit from flexible dosage as opposed to daily medication

You would not qualify for PrEP On-Demand if:

  • You have active hepatitis B
  • You are put in unpredictable situations that put you at risk for HIV transmission (such as not being able to take the first two pills between 2 to 24 hours before sex)
  • Share needles with people who may be HIV positive

Remember, only you and your doctor can determine if PrEP On-Demand is the best option for you. You must consult your physician to discuss if this HIV prevention method is the right fit.


PrEP On-Demand is a great alternative that can be effective at protecting people at high risk of HIV transmission. However, this method is not a good fit for everyone, so it is important to understand your options and discuss HIV prevention tips with a professional.

Our team of navigators at PrEP Daily will help you learn more about PrEP medication, side effects, payment options, and much more. We work with people one-on-one and get them connected with the right doctor to receive a PrEP prescription. Connect with one of our navigators today to get started!