As such, danazol is described as a possessing high affinity for the AR, moderate affinity for the PR and GR, and poor affinity for the ER.[18] As an androgen, danazol is described as weak, being about 200-fold less potent than testosterone in bioassays.[20] The drug can act as both an agonist and antagonist of the PR depending on the bioassay, indicating that it could be regarded as a selective progesterone receptor modulator.[18] Although the affinity and efficacy of danazol itself at the PR are relatively low, ethisterone, one of the major metabolites of danazol, is described as a weak progestogen (and has been employed clinically as a progestogenic contraceptive), and this presumably balances the in vivo progestogenic activity of danazol.[21] The activity of danazol at the ER is considered to be minimal, although at very high concentrations the drug can act significantly as an ER agonist.[18] Danazol is considered to act significantly as an agonist of the GR, and thus, as a glucocorticoid.[18] In accordance, it can suppress the immune system.[5][18][20]