A recent study coordinated by researchers at the Rollins School of Public Health at Emory University and led by the Kaiser Permanente Southern California Department of Research & Evaluation in collaboration with Kaiser Permanente colleagues in Georgia and northern California found a link between cross-sex hormone use in transwomen and an increase in vascular side effects, such as stroke and venous thromboembolism (VTE). These findings are published in the Annals of Internal Medicine. 

The researchers analyzed data from the participating Kaiser Permanente health systems and compared rates of vascular events among 4,690 transgender and gender non-conforming persons to the rates observed in 48,686 cisgender men and 48,775 cisgender women (cisgender references individuals whose gender identity corresponds to their sex assigned at birth). The most striking findings were:

• Rates of VTE in transwomen were nearly twice as high as those among cisgender men and women.
• Rates of stroke and myocardial infarction among transwomen were 80 to 90 percent higher than those observed in cisgender women, but similar to the rates found in cisgender men.  
• The increases in rates of VTE and stroke were more noticeable several years after the initiation of estrogen therapy.
• Data on hormone replacement therapy in postmenopausal cisgender women are likely not generalizable to transgender women

"While our study confirmed elevated risks of certain vascular events related to hormone therapy, these risks need to be weighed against the important benefits of treatment," says Michael Goodman, MD, MPH, professor of epidemiology and corresponding author on the paper.  

The researchers are quick to note that the study represents an early phase of research in this area and that more work is needed in order to better understand the roles of specific hormone formulations, doses, drug combinations and routes of administration.

“Our study represents one of the largest cohorts of transgendered people in the United States," says Darios Getahun, MD, PhD, a research investigator with the Kaiser Permanente Department of Research & Evaluation. “Furthermore, we have carefully validated the transfeminine or transmasculine status of the participants, which is likely to be more valid than other approaches.”

Funding for this project was made possible by the Patient-Centered Outcomes Research Institute (AD-12-11-4532) and the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health (Grant R21HD076387).

About the Kaiser Permanente Southern California Department of Research & Evaluation

The Department of Research & Evaluation conducts high-quality, innovative research into disease etiology, prevention, treatment and care delivery. Investigators conduct epidemiologic research, health services research, biostatistics research and behavioral research as well as clinical trials. Major areas of study include chronic disease, infectious disease, cancer, drug safety and effectiveness, and maternal and child health. Headquartered in Pasadena, California, the department focuses on translating research to practice quickly to benefit the health and lives of Kaiser Permanente Southern California members and the general public.