What If I Miss a Dose of PrEP?


If you want to know how HIV transmission can be prevented, then you may want to discuss taking PrEP with your doctor. PrEP is a prescription medication regimen that has been approved by the FDA to lower the chances of HIV transmission.

The two main medications prescribed for PrEP are Truvada and Descovy. Both of these medications are recommended to be taken once a day for a specified length of time as prescribed by a physician.

However, it is quite common for a person to skip a dosage, whether it be accidently or on purpose. For example, someone may forget the medication at home while they are out or on a trip. Or they may not have time to get to the pharmacy to refill their prescription and miss a full day or two of doses.

If you have missed a dose or are worried that you might in the future, you may be wondering:

  • Could I be more at risk of HIV contraction if I skip a dose of PrEP?
  • What should I do if I miss a day or more?
  • Do I need to start over my PrEP regimen if I miss several days?

There are a lot of questions that people have regarding PrEP and HIV prevention. So, let’s start with explaining just how PrEP works and why it is important to take it as directed by your doctor.

How Does PrEP Work?


HIV is a virus, meaning that once it enters the body, it cannot be removed. Therefore, PrEP is intended to be taken before a person is exposed to HIV so the virus cannot enter and multiply within the body. This is why the scientific term for PrEP is Pre-Exposure Prophylaxis – which essentially means disease prevention before exposure.

It is important to understand that PrEP is not a cure for HIV, but it does help to prevent HIV transmission.

PrEP uses a combination of tenofovir and emtricitabine to prevent HIV transmission. Tenofovir fights off infections to prevent immunosuppression, while emtricitabine prevents HIV cells from growing and reproducing through the body.

PrEP needs to be taken for a certain number of days in order to maximize its effectiveness at preventing HIV transmission. According to the Centers for Disease Control and Prevention, PrEP must be taken for:

  • Seven days to protect from HIV transmission through receptive anal sex
  • Twenty-one days to protect from HIV transmission through receptive vaginal sex or intravenous drug use.

PrEP is typically prescribed to be taken once on a daily basis for a consistent amount of time.

A scientific study determined that PrEP was 99% effective at preventing HIV transmission when it was taken on a daily basis. Patients in the study who took the pills four times a week and missed a few doses were slightly more at risk, as the effectiveness levels dropped to 96%. For patients who took the pill only twice a week, PrEP’s effectiveness was determined to be only 76%.

Therefore, it is incredibly important to take PrEP every day to achieve the highest level of protection against HIV transmission.

What if I Miss a Single Dose?

If you do miss a dose of your PrEP medication, there is not much need for concern. In an interview for the organization Greater Than AIDS, Dr. Demetre explained that skipping just one dose should not have any effect on the level of HIV transmission protection PrEP provides.

Dr. Demetre said,

The more you take [PrEP] on schedule, the more likely it works… shoot for taking it every day. If you miss a dose, don’t beat yourself up, but don’t make a habit out of it.”

He then went on to recommend that a person simply try to get back onto a daily schedule as soon as possible after missing a dose – and maintain consistency as much as possible.

Now it is important to note that it is not recommended to double up on a dosage the next day – just take the missed dosage as soon as you remember or simply start on the scheduled medication for the following day.

What if I Miss Multiple Doses?


Now, the level of effectiveness becomes a much bigger issue if you skip several days in a row or you take PrEP inconsistently. As mentioned before, patients who took PrEP only two to four times a week were at a higher risk of HIV transmission than patients who took PrEP daily.

Therefore, the chances of HIV transmission could be greater if you miss multiple dosages of PrEP – particularly if it is within the first week to twenty-one days of taking it.

It is highly recommended that you reach out to your doctor to let them know how many dosages you have missed – especially if you have engaged in behavior that could put you at risk of HIV contraction.

The leading causes of HIV transmission include:

  • Having unprotected sexual intercourse with a partner who is HIV positive or whose HIV status is unknown.
  • Coming into contact with bodily fluids that could be infected with HIV, such as blood, semen, or vaginal secretions.
  • Sharing intravenous needles with others.

It is incredibly important that you are honest and upfront with your doctor regarding the number of doses you have missed so they can determine the next steps for your PrEP regimen. Your doctor might order additional tests to be sure you are HIV-negative before having you continue with PrEP.


The more consistently you take PrEP, the more protection it will provide to prevent HIV transmission. As with any medication, you should only take as many pills as prescribed by your doctor. If you miss a dose here and there, there is probably nothing to worry about; however, it never hurts to reach out to your doctor to discuss any concerns.

You should also try to find ways to remind yourself to take your PrEP medication on a consistent basis. If you find yourself forgetting to take a dosage or you are simply a bit forgetful, try these tips:

  • Set an alarm or reminder on your phone for the same time every day.
  • Put your medication in a place that you will see it daily, such as next to your toothbrush or on your bedside table.
  • Purchase a daily pill organizer that can be put into your purse or backpack. This also makes it easier to travel, as you can measure out as many doses as you need for a set number of days.

If you have any further questions about HIV prevention or are considering taking PrEP and want to learn more about it, please contact our team at PrEP Daily. We will help you get connected with a navigator who can answer any of your questions.