In the USA, only two in five PrEP users keep taking it over two years

Real-world data from a large American chain of retail pharmacies show that only two in five people keep on taking pre-exposure prophylaxis (PrEP) for two years after starting, researchers report in the Journal of the International AIDS Society this week.

Most studies of PrEP persistence have been for shorter periods of time, but it has been thought that if participants are retained past an initial period on PrEP,  then they are more likely to stick with it. The new study does not support that.

The researchers analysed pharmacy fill records from a random sample of 7148 people who started PrEP at a Walgreens branch in 2015 (perhaps one in ten American PrEP users). Data were collected for two years after starting the preventative treatment. PrEP persistence was defined as having at least 16 days of PrEP medication filled per month for at least three-quarters of the months (e.g. nine months in a year). The threshold of 16 days per month was chosen because dosing at least four days per week has been shown to offer substantial protection against HIV to men who have sex with men.


multivariable analysis

Statistical technique often used to reduce the impact of confounding factors, in order to attempt to identify the real association between a factor of interest and an outcome. 


When using a diagnostic test, the probability that a person who does have a medical condition will receive the correct test result (i.e. positive). 


Studies aim to give information that will be applicable to a large group of people (e.g. adults with diagnosed HIV in the UK). Because it is impractical to conduct a study with such a large group, only a sub-group (a sample) takes part in a study. This isn’t a problem as long as the characteristics of the sample are similar to those of the wider group (e.g. in terms of age, gender, CD4 count and years since diagnosis).


In HIV, refers to the act of telling another person that you have HIV. Many people find this term stigmatising as it suggests information which is normally kept secret. The terms ‘telling’ or ‘sharing’ are more neutral.

sensitivity analysis

An additional analysis of data, also known as a “what–if” analysis, which indicates how robust the study’s results are. Specific assumptions or variables may be changed, to estimate the outcome in a range of scenarios.

The vast majority of PrEP users were men (97%). Most were in their thirties or forties, and 80% had commercial insurance.

  • Over the first 12 months, 56% (4030/7148) were classified as persistent on PrEP.
  • Amongst those who were persistent in the first year, 63% (2521/4030) were persistent during months 13 to 24.
  • Throughout the first 24 months, 41% (2951/7148) were persistent (i.e. they had prescriptions for 18 of the 24 months).

People have ‘seasons of risk’, so not all PrEP users would need to stay on PrEP for the full two years. “But this is unlikely to be the only factor accounting for such high levels of PrEP cessation,” the authors comment. “Such substantial behaviour modification to convert three-fifths of individuals initiating PrEP to be no longer PrEP eligible is highly unlikely.” 

In multivariable analysis, male gender, being 25 years of older, having a copay of $20 or less, having commercial insurance, and attending a community-based specialty pharmacy from the national chain were associated with persistence.

Only 29% of people aged 18 to 25 stayed on PrEP throughout the two years. “Younger individuals may be more likely to experience challenges in a number of areas, including cost navigation, fear of disclosure due to use of parental insurance, limited experience with the healthcare system, and financial barriers,” comment the authors.

Comparable studies of PrEP persistence have not been conducted in settings with fewer financial and administrative barriers to accessing healthcare.

As individuals switching to a different pharmacy could be misclassified as discontinuing PrEP, the researchers conducted a sensitivity analysis which only included the 5837 people who filled a prescription at the chain for something apart from PrEP, after the 24-month study period. This made little difference to the results, indicating that pharmacy switching is not an important factor.


Coy KC et al. Persistence on HIV preexposure prophylaxis medication over a 2-year period among a national sample of 7148 PrEP users, United States, 2015 to 2017. Journal of the International AIDS Society 22:e25252, 2019. (Full text freely available).