These include oral, buccal, sublingual, intranasal, transdermal (gels, creams, patches), rectal suppositories), by intramuscular or subcutaneous injection (in oil or aqueous), and as a subcutaneous implant. The pharmacokinetics of testosterone, including its bioavailability, circulating testosterone levels, metabolism, biological half-life, and other parameters, differ by route of administration. Chemistry
Testosterone is a naturally occurring androstane steroid and is also known by the chemical name androst-4-en-17β-ol-3-one. It has a double bond between the C4 and C5 positions (making it an androstene), a ketone group at the C3 position, and a hydroxyl (alcohol) group at the C17β position. Derivatives
Testosterone esters are substituted at the C17β position with a lipophilic fatty acid ester moiety of varying chain length. Major testosterone esters include testosterone cypionate, testosterone enanthate, testosterone propionate, and testosterone undecanoate. A C17β ether prodrug of testosterone, cloxotestosterone acetate, has also been marketed, although it is little known and is used very rarely or no longer. Another C17β ether prodrug of testosterone, silandrone, also exists but was never marketed, and is notable in that it is orally active. In addition to ester and ether prodrugs, androgen prohormones or precursors of testosterone, such as dehydroepiandrosterone (DHEA), androstenediol, and androstenedione, exist as well, and convert into testosterone to variable extents upon oral ingestion. Unlike testosterone ester and ether prodrugs however, these prohormones are only weakly androgenic/anabolic.All synthetic AAS are derivatives of testosterone. Prominent examples include nandrolone (19-nortestosterone), metandienone (17α-methyl-δ1-testosterone), and stanozolol (a 17α-alkylated derivative of DHT). Unlike testosterone, AAS that are 17α-alkylated, like metandienone and stanozolol, are orally active.
These included decreased levels of total cholesterol, triglycerides, and high-density lipoprotein (HDL) cholesterol, and increased levels of low-density lipoprotein (LDL) cholesterol. However, the changes were small in magnitude, and the long-term significance in relation to cardiovascular outcomes is uncertain. The changes were more pronounced with oral testosterone undecanoate than with parenteral routes, such as transdermal testosterone. Testosterone showed no significant effect on depressed mood anxiety, bone mineral density (BMD), or anthropomorphic measures like body weight or body mass index. Conversely, it was associated with a significant incidence of androgenic side effects, including acne and hirsutism (excessive facial/body hair growth). Other androgenic side effects, such as weight gain, pattern hair loss, and voice deepening, were also reported in some trials, but were excluded from analyses due to insufficient data. The overall quality of the evidence was rated as low and was considered to be inconclusive in certain areas, for instance on long-term safety.A subsequent 2017 systematic review and meta-analysis of studies including over 3,000 postmenopausal women with HSDD similarly found that short-term transdermal testosterone therapy was effective in improving multiple domains of sexual function.