To our knowledge, there are no studies that have been reported in scientific, peer-reviewed journals that suggest that taking such pills might enlarge a man's penis, either in length or circumference.
When drug manufacturers seek approval for their medications from the US Food and Drug Administration (FDA), they have to be able to prove that their product is safe for individuals to take, that it is effective (that is, it does what it is said to do), and they also must document and publish any potential side effects.
We know of no penis enlargement pills that have FDA approval or clearance. As such, there is no way to know whether these pills work (which seems unlikely, or one might guess that a major pharmaceutical company would be manufacturing them by now and turning a huge profit). There is also no way to know whether these pills are safe for individuals to take or whether they are associated with negative side effects. As you may know, some supplements (even herbal types) have been associated with serious - even potentially fatal - negative side effects.
Further, major US medical organizations do not recognize any surgical techniques as being safe and effective for what is called "penile augmentation" (a more clinical term for penis enlargement). Even though you may come across advertisements for penis enlargement surgery, such surgery has been associated with scar tissue which can cause painful erections or even a shortening of the erect penis.
Considering, then, that there do not appear to be any safe and effective methods of penile enlargement, how come they continue to be so widely marketed? Many companies prey on men's and women's concerns about their bodies (and even concerns about masculinity/feminity) - hence the huge market for diet pills, cosmetic surgery, breast enlargement pills, and yes, penis enlargement pills. And yet when it comes to penis size, most men are entirely within the normal range.
The average length of a man’s erect penis is typically about 5 to 6 inches, according to most scientific studies. However, penis size varies widely - some studies show erect length ranging from about 1 or 2 inches to 14 or 16 inches. And there is no "right" length or circumference; each has their advantages or disadvantages. For example, even though men sometimes wish for a larger penis, they may not be aware that men of larger penis sizes sometimes report difficulty finding a sex partner for comfortable oral, vaginal or anal sex, as it may be too painful for their partner. Female partners, for example, can only take so much into their vagina (in an unaroused state, the vagina is about 3-4 inches long; in an aroused state, it expands to about 6 inches long).
Sadly, some companies that sell penis enlargement pills provide inaccurate information on their web sites or other marketing materials suggesting that the average erect penis length is 7 inches. This false information may make men feel shorter than average. Several years ago, we even learned of a company that claimed on their web site that The Kinsey Institute had conducted research proving that their enlargement pills worked, even though we had never conducted such a study.