Testosterone, like many anabolic steroids, was classified as a controlled substance in 1991. Testosterone is administered parenterally in normal and delayed-release (depot) forms. In September 1995, the FDA approved testosterone transdermal patches (Androderm), and many transdermal forms and brands are now available including implants, gels, and topical solutions. A testosterone buccal system, Striant, was FDA-approved in July 2003; Striant is a mucoadhesive product that adheres to the buccal mucosa and provides a controlled and sustained release of testosterone. In May 2014, the FDA approved an intranasal gel formulation of testosterone (Natesto). A transdermal patch (Intrinsa) for hormone replacement in women is under investigation; the daily dosages used in women are much lower than for products used in males. The FDA refused approval for Intrinsa in 2004 stating that more data regarding safety, especially in relation to cardiovascular and breast health, were required.
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.     
The side effects of Androderm can include high blood pressure due to high levels of water retention. However, water retention is highly unlikely due to the low level dosing plans that will be prescribed and easily combatable with anti-estrogen medications if needed. The use of exogenous testosterone can also have a negative impact on cholesterol, particularly in the suppression or reduction of HDL cholesterol. However, therapeutic doses of testosterone to even moderate performance doses do not appear to have a strong, negative statistical impact on cholesterol when testosterone is used alone. When the use of an AI is conjoined with testosterone, this does appear to create a notable impact on HDL reductions. A negative impact cannot occur with the use of a SERM; in fact, SERM’s will actually improve cholesterol levels due to their estrogenic activity in the liver.
While cholesterol issues are possible, they are also easy to avoid. AI’s should not be used unless necessary, but even if necessary healthy cholesterol levels can be maintained with a healthy lifestyle. Limiting saturated fats and simple sugars is a good place to start along with plenty of omega fatty acids. Daily fish oil supplementation is recommended as is daily cardiovascular activity.