Health: In contrast, there is a "fairly rich literature on yohimbine". Subsequent work on yohimbine, while confirming that it behaves as an aphrodisiac in animals, including rats, dogs and golden hamsters, has failed to do so in humans. According to Betz: Clinical efficacy Yohimbine has been used to treat female sexual dysfunction, but there are few reported clinical trials and these do not show it to be better than placebo. On treatment for male erectile dysfunction (ED), a review article by Tam et al. (2001) concluded: Again according to Betz (2010), A 2011 review by Andersson said: Yohimbine has been largely superseded by the PDE5 inhibitor drugs such as sildenafil (Viagra). Prescriptions for it are now rare, and most US pharmaceutical manufacturers have discontinued production of prescription capsules and tablets. Yohimbine has been found to be effective in treating delayed ejaculation in men Yohimbine and dietary supplements In the US, "yohimbe" preparations are sold as a dietary supplements for enhancing libido, for weight loss and as aids for bodybuilding; but "There is virtually no published research on yohimbe which supports these or any other claims". Often, these products explicitly claim to contain yohimbine. Cohen et al. found that samples of brands sold in American brick-and-mortar stores contained highly variable amounts of yohimbine, and sometimes none at all. Labelling claims were often misleading. Similar results have been reported by other laboratories for products sold in the U.S., in other countries and on the internet. One study found that many brands of "yohimbe" might not derive from the P. johimbe tree in the first place. According to yet another source, the yohimbe sold in markets in West Africa, where the tree grows, is frequently adulterated with other species of the genus Pausinystalia; these contain little yohimbine. The amounts of alkaloid found even in genuine P. johimbe bark vary considerably, depending on the source of the bark (roots, stem, branches, height, etc.). Some brands sold over-the-counter were found to contain more yohimbine per serving than a standard pharmaceutical dose; yet, in the US, pharmaceuticals are subject to the strict regulatory regime pertaining to medicines. It is illegal to introduce or deliver "drugs" into interstate commerce without the permission of the FDA. The FDA has asserted that some yohimbine-containing products are "drugs" because they are so promoted as to show "they are intended for use in the cure, mitigation, treatment or prevention of disease":