Table 2:

Overview of relevant studies on tongkat ali and horny goat weed in the treatment of ED

Tongkat Ali
Mechanism of Action (MOA): No clear mechanism of action
Author	Study Type	Outcome Measure	Results
Kotirum et al. (2015)	Meta-analysis	IIEF-5 score	Herbal extract from tongkat ali may have an effect on erectile function, but further studies are required to establish efficacy in treatment of ED
Ismail et al. (2012)	RCT	IIEF-5 score	Men treated with tongkat ali extract reported improved erectile function on IIEF-5 scores than men treated with placebo
Udani et al. (2014)	RCT	Sexual intercourse assessment (SIA)	Significant improvement was reported in multiple subjective erectile function scores in men treated with tongkat ali extract
Horny Goat Weed
MOA: PDE5 inhibitor activity
Shindel et al. (2010)	In vitro rat model	ICP/MAP ratios and NOS expression	Icariin treated rats had higher mean ICP/MAP ratios and penile expression of NOS on Western blot
Zhang et al. (2013)	In vivo rat model	cGMP expression and NOS expression	Icariin increased the expression of cGMP and NOS in diabetic rat models of ED
Long et al. (2018)	In vitro rat model	eNOS coupling	Icariin inhibits eNOS coupling and may be an important mechanism of improving erectile function in rats