Dax Shepard is taking 'heavy testosterone injections,' which are often misused. What experts want you to know.

Actor Dax Shepard has spent years talking openly about sobriety, building his highly successful Armchair Expert podcast around an ethos of vulnerability. Shepard was in recovery for 16 years when he revealed in September that he had relapsed with prescription pain pills, a fact he was reticent to admit publicly but that he decided was relevant for a fanbase who had come to admire his honesty.

In his latest disclosure, the 46-year-old said on his podcast with guests Ashton Kutcher and Mila Kunis that he is using "heavy testosterone injections."

"I spent my whole life as a medium boy," he said after Kutcher remarked on the size of his biceps, "and now I'm a big boy and I like it."

Shepard initially said he was using testosterone to bulk up, but when Kutcher and Kunis expressed concern, Shepard said low testosterone runs in his family and that using it has also helped improve his disposition.

Testosterone is a hormone that helps men maintain everything from muscle strength to facial hair to sex drive. While there are medical reasons for using testosterone, experts say steroid use carries many physical and mental health risks.

"Testosterone is an androgen. It is a powerful steroid that can have a lot of effects downstream, that can impact mood, that can then impact anxiety, that can also itself lead to addiction," said Collin Reiff, an addiction psychiatrist at NYU Langone Health who specializes in substance abuse treatment.

Medical uses for testosterone

Testosterone peaks during adolescence and young adulthood, according to the Mayo Clinic, and declines with age. Shalender Bhasin, a professor of medicine at Harvard Medical School, said testosterone is only approved by the U.S. Food and Drug Administration (FDA) for one clinical use: treatment of hypogonadism in men (a condition where the body does not produce enough testosterone).

Testosterone treatment is also medically appropriate, Bhasin said, as gender affirming care.

Dessa Bergen-Cico, coordinator of the Addiction Studies program at Syracuse University, says the use of alcohol, cannabis, amphetamines and opioids, which Shepard said he abused during his last relapse, can all lower testosterone. Opioid agonist therapies, including methadone and suboxone, can also suppress testosterone. In these cases, experts say testosterone replacement therapy may be recommended, but only under the care of a medical professional.

But even when testosterone is prescribed, it can include a host of dangerous and unwelcome side effects, including an increased risk of blood clots and cardiac problems as well as enlarged breasts and limited sperm production.

While Shepard said testosterone has helped with his mood – he said he "was depressed after (the 2017 film) 'CHIPS'" and now is "on fire to work" – Bhasin said its efficacy in treating major depression has not been shown.

"There is agreement that testosterone does not improve major clinical depression," he said.

Misuse of testosterone

Endocrinologists say the majority of testosterone misuse is driven by body dissatisfaction. Most people who misuse testosterone are young men, almost always weightlifters and recreational bodybuilders who are using testosterone to look leaner and more muscular.

"It's a body image disorder," Bhasin said.

Shepard said he wanted to build muscle mass and has "gained about 24 pounds" by working out "six days a week, lifting heavy (weights)," and using testosterone.

Bergen-Cico said exercise is also viewed in the field of behavioral health as a legitimate addiction, and steroids can exacerbate it.

"The use of steroids can play into that and they can become not addictive in the same way as stimulants and depressants but can play into the same reward and reinforcement pathways in the brain," she said. "It also fosters an increase in adrenaline, aggression and anger, which can have an addictive quality or bite to it."

Michael Parent, a psychology professor at the University of Texas at Austin, said the paraphernalia required to administer testosterone may add an additional layer of risk for some people in recovery.

"If someone is using injectable steroids, that means they have needles around and for some people those needles are triggers," he said. "You might have a stock of hundreds of needles and for some people, it just removes one more barrier from a potential relapse."

Experts stress that no one should use steroids unless under the care of a medical professional. There are significant long-term risks of steroid use.

"One-third of men who use large doses will have profound suppression of testicular function when they stop," Bhasin said. "It can take months or years to recover. Some may not."

This article originally appeared on USA TODAY: Dax Shepard testosterone injections and the risks of steroids