(CNN) -- For thousands of years, explorers have been searching for the Fountain of Youth. Legend has it the elusive fountain contains a restorative source that brings endless vitality to those who drink from its pool.
No one knows what the source is, exactly. It's been called everything from the "water of life" to the "elixir of immortality."
These days, anti-aging specialists simply refer to it as "T."
You'd think T, or testosterone, was pure magic from its advertised results: increased energy, better mental concentration, less fat, more muscle, fewer sleepless nights and a higher sex drive. But experts say altering your body's natural hormone levels can be dangerous if not done properly.
As more FDA-approved products hit the market, the baby boomer generation is taking note. In 2011, consumers spent approximately $1.6 billion on prescription testosterone therapies, almost triple the amount spent in 2006, according to market research company IMS Health.
Dr. Harvey Bartnof is the founder of the California Longevity & Vitality Medical Institute. His practice focuses on age management medicine and hormone replacement therapies for both men and women. He says patients come to him to slow the aging process; they want to remain active and engaged as they grow older.
"We have medications that help people stay alive longer, but the quality of life declines," Bartnof says. "People would rather not go down the pathway of ... mom, dad if they don't have to."
'Viagra for the boardroom'
Testosterone is naturally produced primarily through a man's testes. (The hormone is also found in women, but that's another story.) The hormone helps regulate bone density, fat distribution, muscle strength, red blood cell production, sex drive and sperm production, according to the Mayo Clinic.
Bartnof compares it to oil in a machine -- while other systems make your body "go," hormones such as testosterone grease the wheels so they work smoothly.
The body's production of testosterone peaks in early adulthood and typically declines about 1% each year after age 30, according to the Mayo Clinic website. A low testosterone level is called hypoandrogenism.
Symptoms of hypoandrogenism include insomnia, fewer erections, reduced muscle strength, depression, trouble concentrating and hair loss.
In other words, getting old, John Freiburger quips. The 48-year-old financial planner first started feeling the effects of his age a few years ago.
As the founder of an Illinois wealth management firm, he was juggling multiple clients' portfolios a day. He found his concentration in meetings started to fade earlier, even when he made an effort to hit the gym more often and eat right.
"Being in the business that I'm in, you need to be on top of your game," Freiburger says. "For a lot of men, it's like, 'Oh yeah, I'm getting old.' I'm not very good at accepting that it's the way it needs to be."
Up until a few years ago, testosterone was mostly the choice of competitive body builders and professional athletes. Now, everyone from Wall Street executives to corporate office managers are taking what the media has dubbed "Viagra for the boardroom."
Testosterone replacement therapies come in many forms, according to Nelson Vergel, author of "Testosterone: A Man's Guide." The hormone can be injected into muscle, absorbed through the skin via a cream/gel, or released slowly through a small pellet that's inserted into the body. A doctor does regular blood tests to determine the correct dosage.
Freiburger saw results just two days after beginning his hormone therapy. First, his energy levels skyrocketed. Then he saw an increase in his concentration level at work. Soon after, his libido returned, and within a month he was losing weight and putting on muscle at the gym.
"I'm a better person. I'm a better wealth manager," he said. "(I) have the energy, vitality to go conquer the world."
No magic pill
You've likely read that there's no magic pill for perfect health. While direct-to-consumer marketing may make it seem otherwise, testosterone is no exception, Vergel says.
"I'm just amazed how many men start a hormone without doing research," he says. "It's a wonderful thing to start if you need it. It also has some side effects if not done properly."
The hormone will help you lose weight and build muscle, but not without proper exercise and nutrition. It will also improve your sex drive; what it won't do, Vergel says, is make you into a teenage Casanova.
One of the biggest things to be aware of is that most men never stop testosterone replacement therapy, says Dr. Gregory Broderick, a urologist with the Mayo Clinic.
Once you start, your body begins shutting down natural production of the hormone, thinking it's no longer needed, he explains. This can lead to "shrinkage" of the testicles and a suppression of sperm production.
Broderick says finding a qualified doctor is key. Anti-aging is a new field and most doctors are not trained in hormone therapy, so they learn as they go from pharmaceutical reps and the latest published research. Testosterone replacement therapies often fall to physicians who specialize in "boutique medicine."
Once you find a physician, he or she should screen for prostate cancer before starting treatment. While studies have shown testosterone replacement therapies do not increase the likelihood of developing the cancer, they can encourage tumor growth if a patient already has it.
Broderick recommends getting blood work done every three to four months after beginning testosterone therapy. Men taking testosterone have increased levels of red blood cells, which can lead to complications with circulation, depriving areas of the body of oxygen, and potentially put them at risk for cardiovascular problems.
On average, testosterone replacement therapy costs less than $40 a month. But many baby boomers, such as Freiburger, are using it as part of a more expensive holistic approach to staying healthy into their senior years -- and they say it's worth the cost.
"I would like to have as much quality of life and be as vital as I can as long as the Lord's going to have me on this earth," Freiburger says. "I'm going to take the time and financial resources to try to make that a reality."