The manufacturers of certain testosterone products (., AndroGel and Striant) state that their products are contraindicated in patients with soybean, soy, or soya lecithin hypersensitivity because they are derived partially from soy plants. There is a risk of serious hypersensitivity reactions or anaphylaxis with the use of testosterone undecanoate (Aveed) oil for injection. These allergic reactions can occur after any injection of testosterone undecanoate during the course of therapy, including after the first dose. Observe patients in the healthcare setting for 30 minutes after an Aveed injection in order to provide appropriate medical treatment in the event of serious hypersensitivity reactions or anaphylaxis. The Aveed injection contains benzyl benzoate, the ester of benzyl alcohol and benzoic acid, and refined castor oil. Therefore, testosterone undecanoate use is contraindicated in patients with polyoxyethylated castor oil hypersensitivity, benzoic acid hypersensitivity, or benzyl alcohol hypersensitivity. Patients with suspected hypersensitivity reactions should not be re-treated with testosterone undecanoate injection.
Testosterone cypionate (Depo-Testosterone), testosterone enanthate (Delatestryl), testosterone undecanoate (Aveed), and testosterone pellet (Testopel) are forms of testosterone injection used to treat symptoms of low testosterone in men who have hypogonadism (a condition in which the body does not produce enough natural testosterone). Testosterone is used only for men with low testosterone levels caused by certain medical conditions, including disorders of the testicles, pituitary gland, (a small gland in the brain), or hypothalamus (a part of the brain) that cause hypogonadism. Your doctor will order certain lab tests to check your testosterone levels to see if they are low before you begin to use testosterone injection. Testosterone enanthate (Delatestryl) and testosterone pellet (Testopel) are also used to stimulate puberty in males with delayed puberty. Testosterone enanthate (Delatestryl) injection may be used in certain women with a type of breast cancer called mammary cancer that has spread to other parts of the body. Testosterone should not be used to treat the symptoms of low testosterone in men who have low testosterone due to aging ('age related hypogonadism'). Testosterone is in a class of medications called androgenic hormones. Testosterone is a hormone produced by the body that contributes to the growth, development, and functioning of the male sexual organs and typical male characteristics. Testosterone injection works by supplying synthetic testosterone to replace the testosterone that is normally produced naturally in the body. When used to treat breast cancer, testosterone works by stopping the release of estrogen.
The second theory is similar and is known as "evolutionary neuroandrogenic (ENA) theory of male aggression".   Testosterone and other androgens have evolved to masculinize a brain in order to be competitive even to the point of risking harm to the person and others. By doing so, individuals with masculinized brains as a result of pre-natal and adult life testosterone and androgens enhance their resource acquiring abilities in order to survive, attract and copulate with mates as much as possible.  The masculinization of the brain is not just mediated by testosterone levels at the adult stage, but also testosterone exposure in the womb as a fetus. Higher pre-natal testosterone indicated by a low digit ratio as well as adult testosterone levels increased risk of fouls or aggression among male players in a soccer game.  Studies have also found higher pre-natal testosterone or lower digit ratio to be correlated with higher aggression in males.