Question
Does sexual activity lower testosterone levels in men?
Answer
No.
Explanation
Across the internet, especially in online fora dedicated to discouraging masturbation in young men, it is claimed that masturbation has a long-term detrimental effect on testosterone levels. The idea is that fatigue, low mood, lack of concentration, and other non-specific symptoms, can be linked directly to masturbation.
Studies do not support this claim. Testing 8 males before and after ejaculation following masturbation, a study (Fox, 1972) found that testosterone levels (or T levels) did not show a significant (P > 0.5) difference between samples, finding T levels had increased in 5 subjects and decreased in 3 subjects.
Another study (Exton, 2001) of 10 males showed that after a 3 week sexual abstinence, T levels were increased after those 3 weeks. This study is often used to support the claim that abstinence increases T levels. However, it measured T levels directly before, after, and during the first masturbation after the abstinence, rather than the long term T levels on returning to steady sexual activity (which was intercourse with a partner, 2-3 times weekly). Moreover, the study suggested the increased T levels were a result of psychological factors such as sexual anticipation, rather than orgasm.
Meanwhile, T levels do increase following coitus. A study measuring testosterone samples from 4 couples (Dabbs, 1992) showed that "testosterone increased from before to after coitus, in contrast to changes across the evening on days when there was no coitus. The effect was the same for males and females." Another prolonged study on a single male (Fox, 1972) concluded that "the act of coitus was invariably associated with increased plasma testosterone levels compared with control values".
The greater T level heightening from coitus than from masturbation suggests that orgasm or ejaculation alone are not responsible for the increase.
Sources
Dabbs, J.M., & S. Mohammed, Male and female salivary testosterone concentrations before and after sexual activity (Physiology & Behavior, 1992)
Exton, M.S., et al., Endocrine response to masturbation-induced orgasm in healthy men following a 3-week sexual abstinence (World Journal of Urology, 2001)
Fox, C.A., et al., Studies on the relationship between plasma testosterone levels and human sexual activity (Journal of Endocrinology, 1972)