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A study by the Department of Reproductive Biology, Universidad Autonoma Metropolitana-Iztapalapa found that testosterone levels stayed the same or rised, after various types of sexual encounters in male rats. The more experienced rats had a large increase in testosterone post-ejaculation, which remained even 24 hours afterwards. The sexually inexperienced rats however, had little change in testosterone post sexual encounter. This study suggests that sexual experience and execution, may play a role in the rise of testosterone.
Long term testosterone levels from abstaining ejaculation:
The only study I could find measuring testosterone levels of men who didn't ejaculation for extended periods of time, was research done by chinese researchers, J Zhejiang Univ Sci. 2003 Mar-Apr;4(2):236-40. The study was done on 28 men who were told to not ejaculate for entire week. It was found that for first 6 days testosterone levels did not change. However, on the 7th day of abstaining, testosterone levels jumped up by nearly 50%. It then declined quickly after that day, therefore abstaining from ejaculation had no long term rising effect.
Summary:
What do these studies on animals and humans tell us about the relationship between testosterone and sexual activity? Many people have always assumed that after sexual activity, males experience a drop in testosterone levels. There is no research we could find that points to a significant drop in testosterone post-ejaculation. In fact research tells us that the opposite seems to be true. Men will have significant jumps in testosterone levels from sexually arousing stimuli(and certain other types of stimuli). The research also suggests that sexual encounters and ejaculation, will not effect and may increase, testosterone blood levels.