While significant side effects with testosterone therapy are rare, some of the more common side effects include oily skin, acne, and hair loss if you are prone to balding. Some of the more moderate side effects include a high hematocrit level. Hematocrit is the percentage of red blood cells in your blood. If your hematocrit level is above 54, you may need to switch to cream testosterone replacement, decrease the testosterone dose, or donate blood (therapeutic phlebotomy).
Risks of high hematocrit levels include blood clots, stroke, and heart attack. There is currently no evidence that shows that testosterone replacement can lead to prostate cancer, however, prostate levels are measured with testosterone treatment. Another side effect of testosterone can be the shrinking of the testicles by 10-15%. This can be prevented by taking medication.