Fusion HALOTESTIN (Fluoxymesterone) is a modified form of testosterone.
It differs by:
1) the addition of a methyl group at carbon 17-alpha, which helps protect the hormone during oral administration,
2) the introduction of a fluoro group at carbon 9 (alpha) and 3) the attachement of a hydroxyl group at carbon 11 (beta), which inhibits steroid aromatization.
The latter two modifications also greatly enhance the androgenic and relative biological activity of the steroid over 17-alpha methyltestosterone.