Yohimbe, tribulus, and maca are "natural Viagra"

Several traditional herbs are being studied for their aphrodisiac properties, including yohimbe, tribulus, and maca. Combinations of these are sold as "natural Viagra," but be wary: their effectiveness is unproven, and some, like yohimbe, a type of tree bark, can be lethal if consumed in large quantities. Tree bark? Dude-spring for the Viagra.