Does PrEP Work After 2 Hours?

Key Takeaways

In this article, we'll dive into whether or not PrEP works if taken 2 hours after a possible exposure to HIV.

What is PrEP?

PrEP is an acronym that stands for pre-exposure prophylaxis. Just as its name implies, PrEP is meant to be taken before sexual encounters that might result in HIV exposure. It's an oral medication that comes in tablet form. When taken correctly, it can reduce the risk of sexually transmitted HIV by up to 99%. 

How does PrEP work?

PrEP works by blocking the HIV virus from taking up residence in the white blood cells known as T-cells that it typically targets. When the virus can't infect these cells and reproduce itself, it does not spread in the body. PrEP effectively protects these vulnerable cells, so that users who are exposed to HIV do not contract the virus in the majority of cases.

There are two ways users typically take this drug: daily PrEP and on-demand PrEP. 

Daily PrEP is taken once a day and provides a high level of protection for users who are periodically or regularly exposed to HIV. A Daily PrEP regimen for those who don't know when they may be exposed and don't want to have to plan ahead for exposures. 

An alternative to daily PrEP daily is on-demand PrEP. This schedule is also known as "2-1-1", which refers to the pill schedule. Users should take two PrEP pills 24 hours before possible exposure to HIV. Then, they should take one pill per day for two days (or every day until one day after their last sexual encounter). 

On-demand PrEP is still highly protective, but not quite as much as the daily regimen. When taken correctly, it can reduce the risk of HIV by about 86%. 

Does PrEP work after two hours?

Since it is normally recommended to start taking the 2-1-1 dose of PrEP 24 hours before a sexual encounter, you might be wondering how soon after that initial double dose you can safely have sex. 

Good news: when taking PrEP on-demand, the indication is to take the double dose anywhere between 2 and 24 hours before sex. This means that if you don't take PrEP continuously but you still want to be able to be spontaneous, you don't have to wait a full day to get busy. Just take the double dose, hold off for at least 2 hours, and remember to take the single doses for the next two days. 

Can you take PrEP intermittently?

If you prefer to take PrEP intermittently, you can absolutely do so. The best PrEP schedule for you depends on your lifestyle and personal preferences.

People who want to be able to be spontaneous, or who are regularly exposed to HIV, might prefer to take it daily so that it can just become a habit. This way, you can also maximize your protection. 

Those who may have limited access to PrEP, or who think they may be too forgetful to take it every day, might find the 2-1-1 method is better suited to their lifestyles. 

If you take PrEP intermittently, just remember that you need to take that loading dose of 2 pills every time. If you took PrEP last week, then had a few days off, start again with two pills and wait at least 2 hours to have sex. 

Key takeaways

PrEP drastically reduces the risk of contracting the HIV virus even when exposed to it during anal sex. To ensure the highest level of protection, users should take PrEP daily. This results in a risk reduction of about 99%. 

However, if you don't want to take PrEP every day, you can still reduce your risk by about 86% by taking on-demand PrEP correctly. This means taking two pills between 2 and 24 hours before exposure to the virus. Then, take one pill daily at the same time until one day after the last exposure.

Frequently asked questions

Does PrEP work on the first day?

Yes, PrEP can be taken between 2 and 24 hours before a sexual encounter. This means that users can have sex on the same day they take a double dose of PrEP, as long as they wait at least two hours.

How many pills a day is PrEP?

The number of pills per day of PrEP depends on the usage schedule. When taken daily, PrEP is one pill per day. When taken on-demand, PrEP is two pills on the first day, followed by one pill every day until one day after the last exposure.

Does PrEP work after 1 hour?

No, PrEP does not work after 1 hour. Those using PrEP on demand should wait at least 2 hours before exposure to HIV to increase their protection. 

Medically reviewed by


No items found.
Get on-demand treatment for your everyday health.
Find your treatment