In one study, 11% of transmen who took testosterone developed a condition called erythrocytosis, which impacts red blood cells and slows the blood flow.

In one study, 11% of transmen who took testosterone developed a condition called erythrocytosis, which impacts red blood cells and slows the blood flow. Expand
In one study, 11% of transmen who took testosterone developed a condition called erythrocytosis, which impacts red blood cells and slows the blood flow.

A study [1] of 776 transmen who took testosterone demonstrated that 11% of them developed erythrocytosis, a condition which slows the blood flow, and can lead to headaches, confusion, high blood pressure, nosebleeds, blurred vision, itching and fatigue.

REFERENCES

[1] Madsen, M.C., van Dijk, D. Wiepjes, C.M., Conemans, E.B., Thijs, A. & den Heijer, M. (2021). Erythrocytosis in a Large Cohort of Trans Men Using Testosterone: A Long-Term Follow-Up Study on Prevalence, Determinants, and Exposure Years. The Journal of Clinical Endocrinology & Metabolism 106 (6): 1710–1717. [Link]