Testosterone is significantly correlated with aggression and competitive behaviour and is directly facilitated by the latter. There are two theories on the role of testosterone in aggression and competition.  The first one is the challenge hypothesis which states that testosterone would increase during puberty thus facilitating reproductive and competitive behaviour which would include aggression.  Thus it is the challenge of competition among males of the species that facilitates aggression and violence.  Studies conducted have found direct correlation between testosterone and dominance especially among the most violent criminals in prison who had the highest testosterone levels.  The same research also found fathers (those outside competitive environments) had the lowest testosterone levels compared to other males. 
Commercial synthesis came next. In the 1930s, Austrian chemists were synthesizing male and female hormones from soybean sterols (cholesterol-like substances). This process was expensive because it was hard to separate the sterols from each other. American chemist Percy Julian (1899-1975) discovered a much easier way to separate sterols, which permitted inexpensive synthesis of both progesterone and testosterone. American chemist Carl Djerassi (1923-) is also noted for synthesizing estrone and estradiol (estrogens) from plant materials.
Hormonal output from the thyroid is regulated by thyroid-stimulating hormone (TSH) produced by the anterior pituitary, which itself is regulated by thyrotropin-releasing hormone (TRH) produced by the hypothalamus. The most common hormonal imbalance problems of the thyroid gland consist of an overactive thyroid gland, referred to as hyperthyroidism, and an underactive thyroid gland, referred to as hypothyroidism. Hypothyroidism is treated with hormone replacement therapy (HRT) using a hormone medication such as levothyroxine which is typically required to be taken for the rest of the patient's life. Thyroid hormone treatment is given under the care of a licensed physician and can take a few weeks to become effective in order to alleviate symptoms.