There is no proof to suggest that masturbation can greatly reduce a man's testosterone levels. Studies indicate that testosterone levels in men may temporarily rise after sexual activity, including masturbation. However, testosterone levels can fluctuate throughout the day and can be influenced by various factors such as age, diet, exercise, and overall health. Masturbation is a natural and healthy sexual activity when practiced in moderation, and it does not significantly affect testosterone levels. If you are worried about your testosterone levels, it is recommended that you seek the advice of a healthcare provider.