Fenugreek has a few small, mostly maker-funded trials suggesting modest testosterone and libido effects. What they found, the doses used and how much popular boosters contain.
A few small trials, mostly funded by extract makers, suggest standardized fenugreek seed extract may modestly raise testosterone or improve libido scores in men. The best-known trial (Rao et al., 2016) gave 600 mg a day to 120 men aged 43 to 70 for 12 weeks and reported higher testosterone and better scores on aging-male symptoms. Many testosterone boosters contain far less than that.
Fenugreek (Trigonella foenum-graecum) seeds contain saponins such as protodioscin. These are often said to inhibit aromatase and 5α-reductase, the enzymes that convert testosterone to estrogen and DHT, but that mechanism comes mainly from lab work and hasn't been confirmed in people.
The best-known trial, Rao et al. (2016), gave 600 mg a day of a standardized extract (Testofen) to 120 men aged 43 to 70 for 12 weeks and reported higher testosterone and better scores on aging-male symptoms than placebo. It was funded by the extract's maker. Other small trials have reported mixed results, so fenugreek has real signals from small studies rather than firm proof.
Doses vary widely. Testosil contains 50 mg of fenugreek seed extract per serving, a twelfth of the 600 mg used in the Rao trial, so expect little from its fenugreek; its main ingredients are D-aspartic acid and KSM-66 ashwagandha. TestRX is reported to contain about 300 mg of a different fenugreek extract per serving, about half the trial dose.