Another side effect is that testosterone is converted into dihydrotestosterone or DHT, an excess of which leads to prostate enlargement and hair loss. Another side effect of consuming testosterone propionate or any testosterone based steroid is that the body stops production of testosterone during the period of consumption, since it feels its production is no longer necessary.
Testosterone is normally produced in the testicles in case of men, so the testicles shrink during the phase when testosterone steroid is injected into the body. However, the testicles return to normal size when the steroid is discontinued, and the body starts producing its own testosterone again. A well-known side effect is increase in aggressive behavior of a person. Anti-social behavior and extreme aggression is exhibited by people of low IQ taking steroids .