9.1. Testosterone
One intervention in overweight men noted increases in testosterone with 250mg Coleus Forskohlii (10% Forskolin by weight) over the course of 12 weeks.[30] Although there were significant differences at baseline (5.06+/-1.21ng versus 4.12+/-0.82ng Total Test, 15.90+/-13.39pg v. 13.28+/-7.26pg free test; higher values in Coleus group) increases were still at 6 weeks and 12 weeks in Coleus while no changes occurred in control. Total test increased by 16.77+/-33.77% and free test by 3.47+/-8.10 after 12 weeks, with high inter-individual variance.[30]
The hypothesized mechanism of action is via increasing intra-testicular cAMP levels, which mimick the mechanisms of action of luteinizing hormone in the testicles.[64] LH normally increases cAMP itself, but circumventing LH to increase cAMP can increased steroidogenesis per se.[65][66]Even some other studies investigating herbs likeCordyceps in the testes will use forskolin as a standard by which to compare the efficacy of the newer drugs.[67]
Coleus extract may also induce CYP3A4 in the liver, which theoretically should lead to increased metabolism of testosterone.[62] However, testosterone was not measured in this rat study; isolated forskolin had a much lesser effect.