Definitions: Testosterone is a steroid hormone from the androgen group. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands. It is the principal male sex hormone and an anabolic steroid.
In both men and women, testosterone plays a key role in health and well-being as well as in sexual functioning. Examples include enhanced libido, energy, immune function, and protection against osteoporosis. On average, an adult human male body produces about eight to ten times more testosterone than an adult female body. However the overall ranges for male and female are very wide, such that the ranges actually overlap at the low end and high end respectively. (Source: Wikipedia.)
Please click here for more definitions from other sources.

Forms: Testosterone is usually pescribed to female to male identified people as long as there are no medical contraindication. There are several ways for testosterone to enter the body. The most common way is via injection. A certain amount of the hormone, which is usually suspended in some form of oil, is injected into a muscle from which it is released into the blood stream over a period of time.

Tablets:Striant™ SR (Leaflet)
Many GP's will pescribe Testosterone in tablet form at the start of treatment and then switch over to injections. The reason behind this is that, should there be any unwanted reactions to the hormone itself, treatment can be stopped immediately. Skin reactions that can occur with patches and gels are also eliminated. The tablet is placed on the gum above your teeth where it stays for 12 hours at a time.

Patches: Andropatch® (Leaflet)
Andropatches are skin patches that contain a reservoir of testosterone. The patch is applied to the skin of the back, abdomen, upper arms or thighs. The testosterone is absorbed through the skin from the patch and passes into the bloodstream. The patches are designed to release the testosterone in a manner that mimics the body's natural production of testosterone. One Andropatch is applied every night at approximately 10pm and is replaced after 24 hours. This produces maximum blood levels of testosterone in the early morning hours and minimum levels in the evening, as would occur naturally. (Source: Netdoctor.)

Gels: Testogel® (Leaflet), Androgel (US only)
Gels are sometimes pescibed at the beginning of treatment as only a daily dose is administered rather than a weekly, bi-weekly, monthly or even quarterly dose. It is easy to stop the treatment should there be an adverse reaction to the hormone itself. Gels can also be used to start treatment slowly. Changes are described as slower than on injections.

Injections: Sustanon® (Leaflet), Nebido® (Leaflet)
The most common injection is Sustanon. For general information on testosterone injections from the net doctor click here.

Implants:

Risks:There are some risks or health concerns connected with hormone treatment or the lack of hormones.

Heart Attack:

High Blood Pressure:

Osteoporosis:

Ovarian Cancer:

Thrombosis:

Changes: Once testosterone enters the body on a regular basis as described above, changes will happen to you, some of which are irreversable.

Body:

Hair:

Metabolism:Men usually have a slightly higher body temperature, that is probably why you see boys and men running around in T-Shirts whilst the rest of the population is wearings hats, gloves and scarves. Blood pressure increases which again makes you feel warmer. Usually

Sexual Organs:

Voice:

Blood Tests:

Total Testosterone:

Sex hormone binding globulin (SBHG):

Free Testosterone:

Bioavailable Testosterone: