Oxandrolone is a synthetic androstane steroid and a 17α-alkylated derivative of DHT.    It is also known as 2-oxa-17α-methyl-5α-dihydrotestosterone (2-oxa-17α-methyl-DHT) or as 2-oxa-17α-methyl-5α-androstan-17β-ol-3-one, and is DHT with a methyl group at the C17α position and the C2 carbon replaced with an oxygen atom.    Closely related AAS include the marketed AAS mestanolone (17α-methyl-DHT), oxymetholone (2-hydroxymethylene-17α-methyl-DHT), and stanozolol (a 2,3- pyrazole A ring -fused derivative of 17α-methyl-DHT) and the never-marketed/ designer AAS desoxymethyltestosterone (3-deketo-17α-methyl-δ 2 -DHT), methasterone (2α,17α-dimethyl-DHT), methyl-1-testosterone (17α-methyl-δ 1 -DHT), and methylstenbolone (2,17α-dimethyl-δ 1 -DHT).   
Results wise, users should expect extreme strength increases and weight gain in a relatively short 2-4 week period. Weight gain upwards of 20lbs in 4 weeks is not unheard of with this incredibly potent compound. Although subcutaneous water gain would be minimal, intramuscular water retention should be expected. This is due to inhibition of 11b-hydroxylase and build-up of mineralcorticoids which encourage salt and water retention within the muscles. The most obvious physical effects will be improved vascularity, aggressive muscular pumps, and oily skin.