So when NFG123 mentioned that androgens are antiinflammatory, this is kind of what it means technically. Some steroids seem to have stronger effects than others. So when people say deca improves joints because it makes you hold water, that is nonsense. It is an antiinflmmatory because it suppresses cell mediated immunity, which controls inflammation. it has nothing to do with water.
Why is deca's reputation as an antiinflammatory better than testosterone's for example? My guess is the minimal aromatization and its progestogenic activity. If you link to the article below and open the graphic, you will see a couple of interesting things.
First, progesterone, like testosterone, stimulates humoral immunity (the TH2 mediated response in the graphic) and suppresses cellular immunity (TH1 response). So progesterone has antiinflammatory action.
Second, estrogen exerts a biphasic effect. At low doses it is proinflammatory, stimulating the TH1 arm of the immune system (cellular immunity) and inflammation.
Deca then works both as an androgen and a progestin to quell inflammation. Testosterone, by virtue of its aromatization to estrogen is an inferior antiinflammatory.