One of the fastest growing anti-aging product categories for men is testosterone replacement. Just like women’s levels of key sex hormones decline with age, some men have reduced levels of testosterone as they age. There is some controversy about whether “andropause” is a real phenomenon, but testosterone replacement clearly has benefits for men with a deficiency.  Treating reduced testosterone levels is becoming a big money business.

How big? How about a billion dollars a year and growing:

Sales of testosterone products already on the market have rocketed 25% in the 12 months ending in June, to just under $1 billion. The recession has knocked the wind out of other “lifestyle drugs”—medicines to treat conditions that aren’t life-threatening. Even Pfizer’s blockbuster Viagra fell 8% in the most recent quarter, year over year.

One complication is that plain testosterone can’t be taken in pill form; it gets digested by the liver before it can get into the bloodstream. That means that to be useful, the hormone must either be injected or absorbed through the skin as a gel, cream, patch, etc. Since most people don’t like the idea of giving themselves regular injections if it can at all be avoided, topical applications are most popular. This leads to an interesting problem.

Under a variety of normal circumstances, topical testosterone can get absorbed into the skin of people other than the patient. For example, his wife or kids. As a result, the FDA has issued tips to avoid accidental exposure which include covering the treated area with clothing and taking care to wash the hands after applying the drug. The FDA has also required a “black box” warning on two products. It is important to note that no such warning box will appear on any custom formulation prepared by a compounding pharmacy on your doctor’s orders. It’s still a good idea to follow the FDA tips.

His Take: Big pharma is pushing topical testosterone because it’s an easy sell. They’re not necessarily the best way to increase testosterone, though. Anti-aging doctors generally prefer to use injectable testosterone because it doesn’t rub off or smell bad and provides a very consistent predictable dose regardless of sweat or skin thickness. Newer technologies like implantable pellets that secrete testosterone over time may become the preferred way to replace hormones but for now weekly injections provide the best testosterone results overall.