Asian ginseng  (Panax ginseng) has traditionally been used as a supportive herb for male potency. A double-blind trial found that 1,800 mg per day of Asian ginseng extract for three months helped improve libido and the ability to maintain an erection in men with ED.⁸ The benefit of Asian ginseng confirmed in another double-blind study, in which 900 mg three times a day was given for eight weeks.⁹

Yohimbine (the primary active constituent in yohimbe ) has been shown in several double-blind trials to help treat men with ED;^{10 , 11} negative results have also been reported, however.^{12 , 13} Yohimbe dilates blood vessels and may help, regardless of the cause of ED. A tincture of yohimbe bark is often used in the amount of 5 to 10 drops three times per day. Standardized yohimbe extracts are also available. A typical daily amount of yohimbine is 15 to 30 mg. It is best to use yohimbe and yohimbine under the supervision of a physician.

Dilation of blood vessels necessary for a normal erection depends on a substance called nitric oxide, and nitric oxide formation depends on the amino acid arginine . In a preliminary trial, men with ED were given 2,800 mg of arginine per day for two weeks. Six of the 15 men in the trial were helped, though none improved while taking placebo.¹⁴ In a larger double-blind trial, men with ED were given 1,670 mg of arginine per day or a matching placebo for six weeks.¹⁵ Arginine supplementation was found to be particularly effective at improving ED in men with abnormal nitric oxide metabolism. Although little is known about how effective arginine will be for men with ED or which subset of these men would be helped, available research looks promising and suggests that at least some men are likely to benefit.

Butea superba is a Thai plant that has been used traditionally to increase sexual vigor. In a preliminary trial, 82% of men with erectile dysfunction reported an improvement in erectile function while taking Butea superba for three months.¹⁶ The amount used was 500 mg per day for the first four days, followed by 1,000 mg per day thereafter. The response rate in the placebo group could not be evaluated, because none of the men receiving the placebo returned for their follow-up visit.

Low blood levels of the hormone DHEA (dehydroepiandrosterone) have been reported in some men with ED. In one double-blind trial, 40 men with low DHEA levels and ED were given 50 mg DHEA per day for six months.¹⁷ Significant improvement in both erectile function and interest in sex occurred in the men assigned to take DHEA, but not in those assigned to take placebo. No significant change occurred in testosterone levels or in factors that could affect the prostate gland. Experts have concerns about the safe use of DHEA, particularly because long-term safety data do not exist.

Ginkgo biloba may help some men with ED by increasing blood flow to the penis. One double-blind trial found improvement in men taking 240 mg per day of a standardized Ginkgo biloba extract (GBE) for nine months.¹⁸ A preliminary trial, involving 30 men who were experiencing ED as a result of medication use (selective serotonin reuptake inhibitors and other medications), found that approximately 200 mg per day of GBE had a positive effect on sexual function in 76% of the men.¹⁹

Horny goat weed has long been used in traditional Asian medicine for people with sexual difficulties. It is almost always prescribed in conjunction with other herbs to improve its efficacy and to prevent side effects. People with kidney failure being treated with dialysis had improved sex drive after taking horny goat weed, compared with a similar group not given horny goat weed.²⁰

In a double-blind study, supplementing with the combination of propionyl-L-carnitine (a form of L-carnitine ) and acetyl-L-carnitine (2 grams of each per day) for six months significantly improved erectile function in elderly men with erectile dysfunction associated with low testosterone levels. Propionyl-L-carnitine and acetyl-L-carnitine were significantly more effective than testosterone treatment.²¹

In a double-blind study of men with erectile dysfunction, supplementing with 120 mg per day of Pycnogenol improved erectile function, whereas placebo treatment had no effect.²²

Damiana  (Turnera diffusa) is a traditional herbal treatment for men with ED. However, no modern clinical trials have confirmed its effectiveness.