Anavar oxandrolone:
is an anabolic steroid created by Searle Laboratories under the trademark Anavar, and introduced into the US in 1964. It is taken orally, and unlike other steroids delivered in this manner, most of which are Class II steroids, the majority of its effects are due to reaction with the androgen receptor. In sufficient dosage, Oxandrolone is highly likely to bind well with the receptor, and is therefore a Class I steroid, while having few other side-effects.

The drug was prescribed for a number of medical disorders causing involuntary weight loss, in order to promote muscle regrowth. It had also been shown to be partially successful in treating cases of osteoporosis. However, in part due to bad publicity from its illegal use by bodybuilders, Oxandrolone was discontinued by Searle Laboratories in 1989. It was picked up by Bio-Technology General Corporation who, following successful clinical trials in 1995, released it under the tradename Oxandrin. It was approved for orphan drug status by the Food and Drug Administration (FDA) in treating alcoholic hepatitis, Turner's syndrome, and weight loss caused by HIV. In addition, the drug has shown positive results in treating anaemia and hereditary angioedema. Clinical studies however have shown links between prolonged use of the drug and problems of liver toxicity similar to those found with other 17α-alkylated steroids. Even in small dosages, many users reported gastro-intestinal problems such as bloating, nausea, and diarrhoea.

Before the Controlled Substances Act was passed to restrict the production, sale, and usage of anabolic steroids, Oxandrolone's characteristics lent itself well towards use by female athletes. Its specificity targeting the androgen receptor meant that, unlike many other steroids, it had not been reported to cause stunted growth in younger users, and at typical dosage rarely caused noticeable masculinising effects outside of stimulating muscle growth. In addition, Oxandrolone does not aromatise at any dosage, and is not easily metabolised into DHT or oestrogen. As such, a typical dose of 20-30 mg provided elevated androgen levels for up to eight hours. To increase effectiveness, bodybuilders typically "stacked" the drug with others such as Testosterone, further enhancing body mass gain.