Fusion Stanozolol (Winstrol) is a modified form of dihydrotestosterone.
It differs by:
1) the addition of a methyl group at carbon 17-alpha to protect the hormone during oral administration
2) the attachment of a pyrazol group to the A-ring, replacing the normal 3-keto group (this gives stanozolol the chemical classification of a heterocyclic steroid).
When viewed in the light of 17-alpha methyldihydrotestosterone, the A-ring modification on stanozolol seems to considerably increase its anabolic strength while reducing its relative androgenicity. Fusion Stanozolol (Winstrol) has a much weaker binding affinity for the androgen receptor than testosterone or dihydrotestosterone. At the same time it displays a much longer half-life and lower affinity for serum binding proteins in comparison.