The FDA has found that the vast majority of "male enhancement" and weight loss products sold on Amazon and eBay contain undeclared drugs as ingredients. Buying such products on any website without guidance from a naturopathic physician, herbalist, or other trained natural health care provider is like walking into a minefield.
These tainted products are dangerous for many reasons. First, you don't know the drugs are there in most cases, so you might falsely attribute the benefits of the supplement to the supplement and not the hidden drugs, leading you to take more and risking greater harms. Second, you have no idea what dose of the drugs you are taking. Third, some of these drugs are seriously dangerous at any dose. For instance, sibutramine, an appetite-suppressant, is not legally for sale in most countries due to its dangerous effects on the cardiovascular system. Anabolic steroids are associated with infertility, a three-fold increased risk of dying as well as higher rates of acne, gynecomastia (breast enlargement), and erectile dysfunction. Fourth, there is no way to know if you might have drug-drug interactions, depending on what else you are already taking. Finally, these adulterated products make it seem like all or most natural products for sale are dangerous, when in fact it is only some bad actors selling dangerous garbage. There are plenty of ethical, high-quality companies that would never sell adulterated products.
So if you are having problems with erectile function or want to lose weight, consult with knowledgeable health professionals, and do not trust anything you can buy online for these problems without a practitioner referral. Properly-trained professionals know which brands and products are not adulterated and can help steer you in the right direction.
The FDA's post about this problem can be read in its entirety here (as of 1 Jan 2021).
The FDA's tainted dietary supplements database can be accessed here.