Table 3:

Overview of relevant studies on tribulus terrestris and maca in the treatment of ED

Tribulus Terrestris
Mechanism of Action (MOA): Increased NO activity
Author	Study Type	Outcome Measure	Results
Adaikan et al. (2000)	In vitro rabbit model	Tissue response to electrical field stimulation	Corpora cavernosa of rabbits treated with tribulus demonstrated pro-erectile function
Qureshi et al. (2014)	Meta-analysis	Serum testosterone	Animal models treated with tribulus have increased serum testosterone but no increase was observed in men
Santos et al. (2014)	RCT	IIEF score	No improvement was noted in men treated with tribulus compared to men treated with placebo
Kamenov et al. (2017)	RCT	IIEF score	Tribulus treatment did not increase serum testosterone levels, but did increase IIEF scores
Maca
MOA: No clear mechanism of action
Zheng et al. (2000)	In vitro rat and mouse models	Number of intromissions per 3-hour period	Increased sexual behavior was observed in male mice and rats treated with maca
Zenico et al. (2009)	RCT	IIEF score	Increased erectile function was observed in men treated with maca
Shin et al. (2010)	Meta-analysis	IIEF score	Not enough evidence exists to establish a relationship between maca usage and improved sexual function