“Our study highlights that GLP-1 therapies may not only help with weight and glucose control, but also improve testosterone levels in men with obesity or diabetes — a group at high risk for hypogonadism,” the medical term for low T, says the lead researcher, Shellsea Portillo Canales, MD, an endocrinology fellow at SSM Health St. Louis University Hospital.
“This expands the known benefits of GLP-1s into the domain of reproductive and hormonal health, showing potential for improving quality of life,” Dr. Portillo Canales says.
Testosterone Rose After Participants Took GLP-1s
Research had already shown that weight loss through diet, exercise, or surgery could increase testosterone — but evidence that anti-obesity medications have the same effect has been limited.
For the study, presented recently at the annual meeting of the Endocrine Society in San Francisco, Portillo Canales and her team analyzed the electronic health records of 110 adult men with obesity or type 2 diabetes. Just over half the participants, who were 54 years old on average, had testosterone levels below normal at the start of the study.
All participants were taking a weight loss medication: semaglutide (Ozempic or Wegovy), dulaglutide (Trulicity), or tirzepatide (Zepbound or Mounjaro). The majority (nearly 70 percent) were taking a semaglutide drug. None were receiving testosterone or hormone therapy.
The research team recorded participants’ weight and testosterone levels before they began taking weight loss drugs and then over the course of 18 months.
At the end of the study period, participants lost about 10 percent of their body weight on average — going from 256 to 229 pounds, a loss of roughly 25 pounds.
On average, total testosterone rose by about 18 percent (from 322 nanograms per deciliter [ng/dL] to 380 ng/dL) and free testosterone increased by about 17 percent (from 7 ng/dL to 8.2 ng/dL). Total testosterone refers to the entire amount of testosterone circulating in the blood, while free testosterone refers only to the amount that is not bound to proteins, meaning it’s readily available for use in the body.
Along with the 10 percent weight loss, the proportion of men with normal levels of both total and free testosterone increased from 53 percent to 77 percent — meaning the number of men with low T dropped from about a half to under a quarter.
Portillo Canales says the increases in free testosterone are especially important because free T provides a clearer picture than total T of the true hormonal status across different weight states.
One limitation of the study is that it was a retrospective analysis, meaning it was based on existing medical records rather than results from a randomized clinical trial.
How Does Weight Loss Improve Testosterone Levels?
The new results add to growing evidence that GLP-1s can have a positive impact on testosterone levels for men, says Arthi Thirumalai, MBBS, a clinical researcher who focuses on male reproduction and metabolic health at the University of Washington and the head of endocrinology at Harborview Medical Center in Seattle.
For example, she says, an analysis published earlier this year of seven previous studies found that taking a GLP-1 led to a significant increase in total testosterone for men who were overweight or had obesity.
The primary driver of hormonal improvement is weight loss, not the drugs themselves, says Dr. Thirumalai, who was not involved in the research.
It’s not totally clear why obesity can lead to low T, says Thirumalai. One theory is that fat cells tend to convert testosterone to estrogen and reduce the amount of available testosterone, she says. Men with obesity may also have lower levels of a protein that carries testosterone in the bloodstream, called sex hormone–binding globulin (SHGB). With less of this protein, there is less testosterone available for the body to use.
“Also, inflammation in fat cells causes a release of chemicals that can affect testosterone production,” says Thirumalai.
Why Is It Important to Maintain Normal Testosterone Levels?
Normal testosterone levels support muscle mass, bone strength, sexual health, and overall well-being. Low T, especially in men with obesity or type 2 diabetes, can worsen libido and physical function.
“Improving testosterone can enhance quality of life and possibly reduce health risks associated with low levels,” says Portillo Canales. She says her team didn’t look at these factors in the current study, but they should be examined in future trials.
The bottom line is that GLP-1 therapies may improve testosterone to normal ranges naturally, according to Portillo Canales.
“Men with low T due to obesity may benefit without needing testosterone replacement, but care should be individualized,” she says.
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