Does PrEP work for trans people taking gender-affirming hormones? Yes, says new research

People taking gender-affirming hormones may use PrEP with confidence, said Robert M. Grant, MD, MPH.

A new study published in the journal Clinical Infection Diseases and presented at the AIDS 2020 conference may provide reassurance to transgender people taking gender-affirming hormones and PrEP. In a study with transgender women and transgender men, PrEP did not affect estradiol or testosterone levels after four weeks of daily PrEP use. Conversely, feminizing and masculinizing hormones did not affect the concentration of PrEP drug levels in the blood, and all trans women and trans men in the study had drug levels expected to achieve high protection from HIV. 

“The take away is that transgender men and transgender women may use PrEP with confidence,” said Robert M. Grant, MD, MPH, from the University of California, San Francisco. “PrEP using Truvada did not interfere with hormone therapy like testosterone (for men) and estradiol (for women). Men and women receiving these therapies had similar and protective concentrations of PrEP medicines.”

“We still have a long way to go, but this study was an important step towards meaningful inclusion of trans populations in HIV prevention efforts, and in this case in the use of Truvada for PrEP,” said Marion Pellegrini, NP, clinical manager at San Francisco AIDS Foundation, and coordinator for the study. “And, it addresses some really important questions that trans communities who are taking gender-affirming hormones have about drug-drug interactions, such as how PrEP may impact the effects of hormones and transition-related goals, and how hormones may impact the effectiveness of PrEP in the body. The results of this study, iBrEATHe, provide us with some reassuring evidence.”  

“Historically, transfeminine individuals have been lumped in with cisgender men in this field of research, and transmasculine individuals have been excluded from HIV prevention efforts and HIV prevention research. This exclusion and ‘lumping in’ erodes trust in institutions and providers, so that trans individuals may be less likely to seek PrEP and HIV services. The lack of meaningful representation also impacts the knowledge and attitudes of healthcare providers, so that they may be less likely to identify and prescribe PrEP to trans people,” said Pellegrini.  

The iBrEATHe (Interactions Between Antiretrovirals and Transgender Hormones) Study enrolled 24 HIV-negative trans men taking testosterone (injected testosterone cypionate, injected testosterone enanthate, topical testosterone gel, and implanted testosterone pellets) and 24 HIV-negative trans women taking oral or injected estradiol. All participants had been stable on their hormone therapy for at least six months prior to joining the study. 

After enrolling in the study, all participants started daily oral PrEP with Truvada (tenofovir diphosphate and emtricitabine) with daily observed dosing in-person or by video with a member of the study team. Blood samples were taken after 1, 2, 3, and 4 weeks. 

Nearly all PrEP doses were reported to have been taken during the study (99.5%), with 96.9% observed by video and 1.5% observed in-person. 

Hormone levels on PrEP  

After four weeks on PrEP, there was no change in blood estradiol concentrations in either trans women or trans men. As expected, estradiol concentrations among trans women were higher both at baseline and week 4 compared to trans men. 

iBrEATHe hormone concentrations
Hormone concentrations before and after FTC/TDF PrEP dosing. Serum estradiol concentrations (Fig 1) and total testosterone concentrations (Fig 2) are shown before PrEP dosing and after 4 weeks of directly observed daily dosing among transgender men (TGM) and transgender women (TGW). SOURCE: Grant et al., AIDS 2020.

Similarly, there were no changes in blood testosterone concentrations after four weeks on PrEP for either trans women or trans men. As expected, testosterone concentrations among trans men were higher at both baseline and week 4 compared to trans women. 

PrEP drug levels

Levels of tenofovir diphosphate (TFV-DP, one of the drugs in PrEP) were measured in dried blood spots from samples taken after four weeks on PrEP, and compared to levels in cisgender men and women who had also completed four weeks of directly observed PrEP dosing. 

During the first two weeks on PrEP, there were no differences in drug concentration levels between trans men, trans women and cis men. The increase in drug concentration levels between weeks 2 and 4 was slightly higher among cis men. After 4 weeks, trans women and cis men had comparable drug concentration levels, but drug levels among trans men were slightly lower compared to cis women. 

Importantly, all people in the study were anticipated to reach drug levels that have been shown to be “highly protective” against HIV. 

Implications of the study 

In addition to providing reassurance to individuals taking gender-affirming hormones with daily PrEP, the study opens the possibility of PrEP 2-1-1 dosing for trans individuals taking hormones who may be exposed by HIV through anal sex. PrEP 2-1-1 dosing, also called event-based dosing or PrEP on-demand, involves taking PrEP medication around the times of anal sex instead of daily.

“Some other studies in trans women had suggested that PrEP drug concentrations were too low to use in 2-1-1 dosing, but those studies could have been biased by substantial differences in adherence, body weight, and age. These new data controlled these differences,” said Grant.

San Francisco AIDS Foundation’s clinic, the site where the iBrEATHe Study was conducted, now offers PrEP 2-1-1 dosing to trans clients who may be exposed to HIV by anal sex. PrEP 2-1-1 dosing is not recommended for protection during front hole or vaginal sex.   


Grant, R.M. and colleagues. Sex Hormone Therapy and Tenofovir Diphosphate Concentration in Dried Blood Spots: Primary Results of the iBrEATHe Study. Clinical Infectious Diseases, August 2020. 

About the author

Emily Land, MA

Emily Land, MA is a writer and the Vice President of Public Affairs at San Francisco AIDS Foundation.