Cardiovascular disease, and its underlying pathological process atherosclerosis, is an important cause of morbidity and mortality in the developed and developing world. Coronary heart disease in particular is the commonest cause of death worldwide (AHA 2002; MacKay and Mensah 2004). As well as increasing with age, this disease is more common in the male versus female population internationally, which has led to interest in the potential role of sex hormones in modulating risk of development of atherosclerosis. Concerns about the potential adverse effects of testosterone treatment on cardiovascular disease have previously contributed to caution in prescribing testosterone to those who have, or who are at risk of, cardiovascular disease. Contrary to fears of the potential adverse effects of testosterone on cardiovascular disease, there are over forty epidemiological studies which have examined the relationship of testosterone levels to the presence or development of coronary heart disease, and none have shown a positive correlation. Many of these studies have found the presence of coronary heart disease to be associated with low testosterone levels (Reviews: Jones, Jones et al 2003; Jones et al 2005).

Men who watch a sexually explicit movie have an average increase of 35% in testosterone, peaking at 60–90 minutes after the end of the film, but no increase is seen in men who watch sexually neutral films.[43] Men who watch sexually explicit films also report increased motivation, competitiveness, and decreased exhaustion.[44] A link has also been found between relaxation following sexual arousal and testosterone levels.[45]
Low testosterone levels have a dramatic effect on emotional state. The American Academy of Family Physicians lists depression, impaired cognition and increased fatigue as symptoms of low testosterone production, or hypogonadism. Testosterone replacement therapy for hypogonadal men has successfully reduced negative moods relating to fatigue and depression while increasing feelings of self-esteem. Increasing testosterone in eugonadal men has also shown positive emotional benefits such as increased feelings of self-esteem and reduction of fatigue. The intensity of these benefits is dependent on dosage; a wide body of literature on testosterone increase has shown that at higher dosage aggression, and aggressive response, can become pronounced.
Increased testosterone can have an impact on body composition. Possible benefits include gains in lean muscle mass, reduced body fat and increased bone density. Testosterone inhibits uptake of triglycerides and increases lipid mobilization from adipose tissue, and the increase or decrease of testosterone will usually have an inverse effect on fat stores, with higher testosterone generally causing a decrease in body fat. "The Journal of Clinical Endocrinology and Metabolism" published a study in 2007 that showed decreases in body fat and increases in lean mass in HIV-positive obese men given testosterone therapy. In 1989, a study of the effects of testosterone on muscle mass at the University of Rochester School of Medicine and Dentistry suggests that increasing testosterone increases protein synthesis in muscles. Body composition changes from increased testosterone were also demonstrated in a 1999 study at the School of Exercise Science and Sports Management, Southern Cross University in Australia performed on male weight-training subjects, which showed increases in arm girth and body weight and decreased body fat following a 12-week cycle of testosterone enanthate.

Common side effects from testosterone medication include acne, swelling, and breast enlargement in males.[10] Serious side effects may include liver toxicity, heart disease, and behavioral changes.[10] Women and children who are exposed may develop virilization.[10] It is recommended that individuals with prostate cancer not use the medication.[10] It can cause harm if used during pregnancy or breastfeeding.[10]
Although some men believe that taking testosterone medications may help them feel younger and more vigorous as they age, few rigorous studies have examined testosterone therapy in men who have healthy testosterone levels. And some small studies have revealed mixed results. For example, in one study healthy men who took testosterone medications increased muscle mass but didn't gain strength.
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