Former MMA champion Mark Kerr, known as “The Smashing Machine,” has opened up about the devastating long-term effects of his career, revealing that his testosterone levels plummeted to those of a prepubescent child following years of PED use and repeated head trauma.
In a candid interview, Kerr disclosed that when he finally got tested, his testosterone levels registered at just 82 – a figure so low it essentially rendered him “not a human being,” as he put it. To put this in perspective, a typical adult male’s testosterone level ranges from 300-1000 ng/dL, making Kerr’s reading comparable to that of a child who hasn’t yet reached puberty.
“I had no idea,” Kerr admitted. “It’s like a prepubescent child. I had a friend that kept asking me, ‘Hey, let’s go out,’ and I’m like, ‘No, I just got to go home.'”
A cardiologist friend eventually convinced him to get tested, and the results were severe.
“The second he gets back, he calls me up. He’s like, ‘Okay, I understand why you are where you are because it’s a huge part of just drive and a huge part of vitality.'”
The former NCAA wrestling champion and four-time ADCC world champion attributes his hormonal devastation to a combination of factors from his MMA career. The repeated concussions he sustained during his time competing in Pride FC and other organizations contributed significantly to his condition, as head trauma is known to disrupt the body’s hormone production.
“You get all these concussions and then symptoms of concussions are low testosterone, mood swings, all this stuff,”
he explained.
“I wanted Pride to be built off of my efforts,” Kerr explained about his motivation to stay constantly available for bouts. “So availability was one thing that I’m like, I got to be available. Ask me to compete, I’m available. Didn’t matter what was going on”
This mindset led him down a path of dependency that would haunt him for years.
The low testosterone manifested in multiple ways that severely impacted Kerr’s quality of life. He experienced chronic sleep problems, anxiety, irritability and a complete loss of motivation.
“I was restless, irritable, discontent,” he recalled. “I’d lay down, anxiety would kick in, my head would start talking to me. I was afraid to go to sleep because I had anxiety about not sleeping.”
Once Kerr began testosterone replacement therapy and addressed his hormonal imbalance, the transformation was dramatic. His sleep improved, his anxiety decreased and for the first time in years, he felt genuinely okay.
“Everything else just started kind of stacking on top of it,”
he said of the recovery process.
Many MMA stars who used PEDs earlier in their careers end up requiring testosterone replacement therapy (TRT) as they age due to long-term disruption of the body’s endocrine system. PEDs work by artificially increasing circulating androgens, which signals the hypothalamus and pituitary gland to reduce or shut down natural testosterone production—a process known as hypogonadotropic hypogonadism. Over time, this suppression can cause the testes to atrophy and lose their ability to produce adequate testosterone even after PED use stops. Compounded by natural age-related declines in hormone levels, former users often experience extreme fatigue, muscle loss, mood disturbances, and metabolic slowdown that are more severe than in non-users of the same age. As a result, TRT becomes a medical necessity rather than a performance enhancer, essentially replacing a hormonal system that was permanently downregulated by years of exogenous manipulation.
