Anabolic and androgenic effects
Relative androgenic:anabolic
activity in animals[16]
Preparation Ratio
Testosterone 1:1
Methyltestosterone 1:1
Fluoxymesterone 1:2
Oxymetholone 1:3
Oxandrolone 1:3–1:13
Nandrolone decanoate 1:2.5–1:4

As the name suggests, anabolic-androgenic steroids have two different, but overlapping, types of effects: anabolic, meaning that they promote anabolism (cell growth), and androgenic (or virilizing), meaning that they affect the development and maintenance of masculine characteristics.

Some examples of the anabolic effects of these hormones are increased protein synthesis from amino acids, increased appetite, increased bone remodeling and growth, and stimulation of bone marrow, which increases the production of red blood cells. Through a number of mechanisms anabolic steroids stimulate the formation of muscles cells and hence cause an increase in the size of skeletal muscles leading to increased strength.

The androgenic effects of AAS are numerous. Processes affected include pubertal growth, sebaceous gland oil production, and sexuality (especially in fetal development). Some examples of virilizing effects are growth of the clitoris in females and the penis in male children (the adult penis does not grow even when exposed to high doses of androgens), increased growth of androgen-sensitive hair (pubic, beard, chest, and limb hair), increased vocal cord size, deepening the voice, increased libido, suppression of natural sex hormones, and impaired production of sperm.

The androgenic:anabolic ratio of an AAS is an important factor when determining the clinical application of these compounds. Compounds with a high ratio of androgenic to a anabolic effects are the drug of choice in androgen-replacement therapy (e.g. treating hypogonadism in males), whereas compounds with a reduced androgenic:anabolic ratio are preferred for anemia, osteoporosis, and to reverse protein loss following trauma, surgery or prolonged immobilization. Determination of androgenic:anabolic ratio is typically performed in animal studies, which has led to the marketing of some compounds claimed to have anabolic activity with weak androgenic effects. This disassociation is less marked in humans, where all anabolic steroids have significant androgenic effects.

A commonly used protocol for determining the androgenic:anabolic ratio, dating back to the 1950s, uses the relative weights of ventral prostate (VP) and levator ani muscle (LA) of male rats. The VP weight is an indicator of the androgenic effect, while the LA weight is an indicator of the anabolic effect. Two or more batches of rats are castrated and given no treatment and respectively some AAS of interest. The LA/VP ratio for an AAS is calculated as the ratio of LA/VP weight gains produced by the treatment with that compound using castrated but untreated rats as baseline: (LAc,t–LAc)/(VPc,t–VPc). The LA/VP weight gain ratio from rat experiments is not unitary for testosterone (typically 0.3–0.4), but it's normalized for presentation purposes, and used as basis of comparison for other AAS, which have their androgenic:anabolic ratios scaled accordingly (as shown in the table above). In the early 2000s this procedure was standardized and generalized throughout OECD in what is now known as the Hershberger assay.