Is human growth hormone the fountain of youth or a dangerous drug?
Professional athletes are banned from using human-growth hormone because it is a performance-enhancing drug.
It's the same controversial substance legendary NFL Quarterback Peyton Manning has denied using after Al Jazeera accused that HGH was delivered to his 40-year-old wife Ashley in a controversial documentary, The Dark Side.
Endocrinologist Dr. Stuart Weinerman told INSIDE EDITION it's not uncommon for women to use HGH.
"There are claims that it is truly anti-aging, that it reduces aging, increases longevity although there is no hard evidence to support it," he said.
TV personality Suzanne Somers swears by it, telling IE in 2012: "The reason I take it, I want to keep my bones strong, I want to keep my muscles strong."
One man, Dr. Jeffery Life, looks every bit his age but his body seems decades younger. The 77-year-old said it's thanks in part to human-growth hormone.
Life is a walking billboard for an age management medical practice based in Las Vegas called Cenegenics.
"I actually feel better than I did when I was in my 30's," he told IE in 2012.
Life said he took basic steps to transform his body including exercise and vitamin supplements, but there were also controversial measures. He told IE that he took testosterone and HGH.
But using HGH may have a dark side.
In 2007, Life's former colleague, Dr. Allan Mintz, died shortly after undergoing a biopsy on his brain at 69 years old.
Dr. Life says Dr. Mintz's death had nothing to do with HGH.
Weinerman says the side effects of HGH are not fully researched.
"We have no idea what it does to long term risk of heart disease or cancer or arthritis," he said.
Life said he hasn't experienced any side effects. He has been happily married to a woman almost 20 years younger.
"We're all going to age, everything ages, but we don't have to get old," he said.