A new Al Jazeera documentary, titled "The Dark Side," claims to reveal the performance-enhancing health clinic that reportedly supplied NFL quarterback Peyton Manning with steroids and human growth hormone (HGH). Although Manning has vehemently denied these claims, the documentary, which is the result of an in-depth investigation, does have some eye-opening evidence to back allegations.

For the documentary, journalist Liam Collins went undercover as a 2016 Olympic hopeful in an effort to expose a serious, well-connected performance-enhancing drug trade. While undercover, Collins met with Charlie Sly, a pharmacist in Austin, Texas, who revealed he was part of a medical team at the Guyer Institute, an Indiana-based anti-aging clinic that helped Manning recover from neck surgery in 2011. According to Sly, part of the recovery process involved shipping HGH, which was banned by the NFL since 1991, to Manning’s wife, Ashley. Although Manning’s management has called the claims “outrageous and wrong,” they have not denied that Ashley was shipped growth hormones, The Huffington Post reported.

We all naturally produce HGH to help with cell growth and regeneration, with women producing about twice as much of the hormones than males. According to Muscle and Fitness, our HGH levels peak during puberty and decline starting in our early 20s, but taking the hormone in supplement form can help quickly build muscle, get rid of fat, and increase libido. Although in the U.S. the drug can only be obtained with a doctor’s prescription and is banned by many professional sports organizations, such as the NFL and the Olympics, as revealed in the documentary, some medical professionals can help athletes not only obtain the drugs, but also pass sophisticated drugs tests.

To learn more about Al Jazeera's investigation, check out the full length documentary above.