The airwaves and Internet are full of advertisements for "male enhancement" products: magic pills "guaranteed" to enlarge your penis and increase your sex drive.
For example, ExtenZe, perhaps the most commonly advertised product of this nature, purports to do the following:
Generates Rock Hard Erections
Stop Premature Ejaculation
Increase Stamina and Endurance
Treats Erectile Dysfunction
Increase Size And Girth
Generate Mind Blowing Orgasms
Increase Your Libido
Many of these claims are testable. Obviously you can measure size differences, but things like premature ejaculation, stamina, and endurance can be tested by measuring the amount of time it takes to ejaculate before and after using the product, with normalization of the related external factors. Of course, others aren't. I know what a "mind blowing orgasm" is, but I certainly couldn't explain it scientifically. (Nor have I ever needed to take anything to experience one!)
Regardless, none of these products are FDA approved, and there doesn't seem to be much research proving or refuting their claims. Some even say many of these products are dangerous.
But, many such sites appear to be veiled advertisements for a different product or technique that they purport to not be dangerous. For instance, an organization called Male Enhancement Research, which is one of the top Google hits for male enhancement, states the following:
“Do male enhancement products really work? The fact is that many male enhancement companies are trying to sell products that do not work, and these so called natural male enhancement products have actually been known to cause harmful side effects such as high blood pressure, or worse!”
Yet, the very next page shows this table that lists one product as 98% successful with results "up to 48%":
Between websites offering these products and websites of dubious objectivity, like the aforementioned, it is incredibly hard to find independent research on products like these.
Is there any evidence that these products work? On the other hand, is there any research that indicates that these products might be harmful?
In order to look at this question with a good, critical eye, let's first talk about what these claims actually mean. One of the big problems with products that claim to help male performance is that they claim to be able to deal with things related with multiple biological systems. For example, blood flow to the penis requires other parts of your body to perform well that are unrelated to the aspect of your sexual functioning that helps you last longer.
When male enhancement products make the claims you're talking about, they are actually claiming that they can:
Increase time that an erection can
last by altering the variables that
affect the erection and prolonging
the amount of time between initial
stimulation and ejaculation.
Change the person's physiology so
that they can perform better in the
act of copulating.
Address issues that could cause
Alter the individual's physiology so
that their orgasmic experience is
Increase an individual's sex drive.
The first item, alone, is a pretty significant medical task. The penis may seem like a pretty basic structure on a creature, but there are multiple types of tissues in there. Medical science struggles with diseases that can be treated by altering tissue on very basic levels. Infants who are born with weak hearts or lungs would benefit tremendously if we could simply give them a medication and make them all better by strengthening just their heart or just their lungs. Instead, though, because we can't target the heart, specifically, we give them a general medication that alters their entire body, usually, steroids. So, the very first claim that male enhancement products make is that they've accomplished something that doctors have needed for years: growing only a specific region of the body without altering the rest. Not only does the claim that these products make target a specific part, they claim they've managed to find a single medication that targets only a specific group of organs on only one region of the body. That's kind of like saying they could give you a pill and make only your left hand grow and nothing else.
The second claim is even more complicated than the first. The length of time that a man can hold an erection relies heavily on multiple factors from what he's thinking about, at the time, to if he's being stimulated and how sensitive his penis is in the moment. Genital sensitivity, itself, is inconsistent. This is why extended stimulation of the same pattern does not produce consistent biological responses. In other words, if an individual touches their penis in the same exact way for several minutes, the penis will become desensitized and the erection won't stay unless something changes. The effects of sensitization and desensitization can be seen in Pavlov's work with dogs, but the same mechanisms exist in humans and can happen, similarly, to any stimuli, from tactile senses to smell. Beyond that, most men experience variation in their erection just based on what they're thinking. While erections can be unpredictable, so can moments when an erection fails. Furthermore, during pauses in a sexual experience, the stimulation of the man's genitals is likely to vary as well, so that it is common for a man to lose and regain his erection while he's having sex.
The main problem with the third claim is that it is making a claim about something that is barely related to the act of having sex. A person's stamina and endurance, even during sex, has to do with their overall health. A person in poor health is less likely to have very good stamina or endurance during sex, whereas a person in excellent health is more likely to last longer. By claiming that they can improve something like this, the claim that is really being made is essentially that this is an overall miracle drug, capable of, at least for the short-term, curing what ails ya.
Erectile dysfunction is typically a side-effect of various types of medical conditions from diabetes to prostate cancer. Typically, treatment for erectile dysfunction is treatment for the possible causes plus a treatment of the symptom. In order to treat erectile dysfunction, the main approved treatments are Viagra and Cialis. These two medications are not automatic cures for the problem, though. They only make the process of getting an erection easier. Other factors, such as stimulation, as mentioned above, still apply to the variations in the kinds of erections one might get when using a drug that treats erectile dysfunction. Even drugs designed and approved by the FDA to treat problems with penile function don't make claims as extreme as penis enhancement drugs. Viagra blocks a chemical that is responsible for reversing an erection. In order for someone to obtain an erection, stimulation is still necessary and blood still has to enter the penis.
It is more difficult to think critically about the sensation one feels during orgasm from one sexual experience to the next (requiring most studies on male orgasm to involve internal devices, like anal probes). Little variations from what is said to how it is said to what position a couple is using can change the sensations one feels during sex and even affect orgasm. This isn't surprising, since vocalizations have shown to be factors that can change if a mate ejaculates or not in a range of species from mice to macaques. Furthermore, the claims made regarding orgasm sensations ignore the fact that males have different phases of orgasm which, if interrupted, can also change the sensation of their orgasm. Men are capable of blocking the second phase of orgasm, which is suspected (but still needs tested) to result in additional pressure below the bladder, due to the pooling of liquid, to increase the sensation of another orgasm if it is attempted very soon after.
The last claim, that sex drive will increase with use of a penis enhancer is also difficult to test. There is no evidence that a penis enhancer can do this. Again, multiple factors can affect sex drive, including one's mental and physical health. Anything from blood sugar levels(1) to iron levels to depression can affect an individual's sex drive. A doctor trying to address the issue of someone's sex drive is more likely to look into those factors before ever suggesting a treatment of just the symptom of a decreased sex drive.
With all that said, you're correct that there haven't been many studies on the effectiveness for these treatments. The reason, though, is because of what I've stated above. The claims made by those producing these pills are pretty unreasonable. That's why Steve Warshack and some of his family were found guilty of crimes related to the production and distribution of Enzyte, an herbal pill which claimed to be capable of penis enhancement and famous for the Smilin' Bob commercials. To complicate matters, the FDA has more relaxed rules when it comes to "natural remedies" and "herbal" supplements, which makes it easier for a company to make claims about a product and face fewer penalties, even when their claims are found to be wrong (which is why the Enzyte case was triggered by the Better Business Bureau and not the FDA).
Because most of the products claiming to be male enhancement products are unregulated, they fall into the same categories as other types of herbal treatments and should be approached with caution because of lack of testing and the consequences of introducing things into your body that could be potentially dangerous or that your doctor may not have enough information about. This study addresses some of that problem well:
Unfortunately there is no universal regulatory system in place that insures that any of these plant remedies are what they say they are, do what is claimed, or most importantly are safe. Data will be presented in this context, outlining how adulteration, inappropriate formulation, or lack of understanding of plant and drug interactions have led to adverse reactions that are sometimes life-threatening or lethal.
As far as potential harm that these products may cause, we don't yet know. These products do prey on individual insecurities, but if we use that as a measure of harm, we'd have to also consider many cosmetics to be harmful as well (though, many cosmetics do exactly what they claim, so there is at least that difference in favor of them over male enhancement products). Most male enhancement products are very expensive and a person particularly concerned with their sexual performance is vulnerable to companies which may sell him ineffective products as he ignores the possibility that his sexual concern may be an indication of a medical problem. So far, this type of harm is not easily measured and we're not likely to ever find the kind of data we would need to confirm or deny it.
So, basically, the answer is that we can't really know if male enhancement products work, but it is very unlikely when we consider the claims that are made. Also, with lack of proper studies on the products, we can't really know what kind of harm they may cause to individuals, physically, and other possible harmful elements are, thus far, not even measurable.
(1) A recent study has found that the decrease in sex drive in diabetics is possibly related to the decrease in sexual function and may not be a symptom, itself.
An extract from the class-action statement is given below (my emphasis to highlight the false claims):
A proposed $6 million settlement has been reached in a class action lawsuit against the manufacturer of “male enhancement” product ExtenZe. If you’ve purchased ExtenZe within the past five years, you may be able to receive a cash refund or free ExtenZe merchandise under the class action lawsuit settlement.
The ExtenZe class action lawsuit accuses Biotab Nutraceuticals, Inc. and several other defendants of making false claims in their advertising, promotion, marketing and labeling of ExtenZe. According to the ExtenZe class action, the defendants’ claims that ExtenZe will increase the size of a man’s penis are allegedly false and not supported by any credible scientific evidence. The lawsuit further charges that the defendants are already in violation of a court-ordered injunction prohibiting such claims. The case is entitled Williams, et al. v. Biotab Nutraceuticals, Inc. et al.