Mounjaro and Testosterone: How Weight Loss on Tirzepatide Can Restore Male Hormones

Low testosterone is one of the most common hormonal problems in men with obesity, affecting anywhere from 30 to 79 per cent of those carrying significant excess weight. For many of these men, the connection between body fat and falling hormone levels creates a vicious cycle that is difficult to break with willpower alone. Mounjaro (tirzepatide) is now showing promise not only as a weight-loss treatment but also as a way to restore testosterone naturally, without the need for hormone replacement.

In this article, we look at the clinical evidence linking tirzepatide to testosterone recovery in men, explain why excess body fat suppresses male hormones in the first place, and outline what this means for men considering doctor-led Mounjaro treatment at CutKilo.

Yes. A 2025 study presented at ENDO 2025 (the Endocrine Society annual meeting) found that men with obesity and metabolic hypogonadism treated with tirzepatide had greater increases in endogenous testosterone production than men treated with testosterone replacement therapy (TRT) or lifestyle changes alone. In a separate analysis of 110 men, the proportion achieving normal testosterone levels rose from 53 per cent to 77 per cent after 18 months on GLP-1 medication. However, these effects are driven by weight loss and fat reduction rather than a direct hormonal action of the drug itself.

The relationship between excess body fat and low testosterone is well established in endocrinology. Understanding the mechanism helps explain why weight loss on Mounjaro can reverse the problem.

Adipose (fat) tissue contains an enzyme called aromatase (CYP19), which converts testosterone into oestradiol, a form of oestrogen. The more body fat a man carries, the more aromatase activity there is, and the more testosterone is converted. As a result, oestradiol levels rise while testosterone falls.

Furthermore, the relative excess of oestradiol feeds back to the hypothalamic-pituitary axis in the brain, suppressing the release of luteinising hormone (LH) and follicle-stimulating hormone (FSH). These are the signals that tell the testes to produce testosterone and sperm. In other words, the brain receives a false signal that enough sex hormones are circulating, and it dials down production.

This creates what endocrinologists call a “vicious cycle”: low testosterone promotes further fat accumulation (particularly visceral fat around the organs), which in turn drives even more aromatase activity and deeper hormonal suppression. Consequently, many men find it nearly impossible to lose weight through diet and exercise alone when their testosterone is already low.

The most significant evidence comes from a controlled pilot study led by Rossella Cannarella and published in Reproductive Biology and Endocrinology in 2025. The study enrolled 83 men with obesity (mean BMI 34.9), confirmed metabolic hypogonadism, and insulin resistance.

Participants were divided into three groups: tirzepatide treatment, transdermal testosterone replacement therapy (TRT), and no pharmacological intervention (lifestyle advice only). After two months, the tirzepatide group showed greater improvements across several measures compared to both other groups.

Specifically, the men on tirzepatide experienced greater weight loss, increased endogenous testosterone production, and improved erectile function scores. In contrast, TRT suppressed gonadotropins (LH and FSH), meaning the body’s own testosterone production was shut down rather than restored. Tirzepatide, on the other hand, appeared to restore the hypothalamic-pituitary-gonadal axis to normal function.

Additionally, a retrospective study from Saint Louis University Hospital analysed 110 adult men with obesity or type 2 diabetes taking GLP-1 medications over 18 months. The proportion of men with normal levels of both total and free testosterone rose from 53 per cent to 77 per cent during treatment.

Tirzepatide does not act directly on the testes or the hypothalamic-pituitary-gonadal axis. Instead, it works through an indirect but powerful route: by reducing the volume of adipose tissue that drives the hormonal suppression in the first place.

In the SURMOUNT-1 trial, participants receiving the highest dose of tirzepatide lost an average of 22.5 per cent of their body weight over 72 weeks. This level of fat reduction substantially lowers aromatase activity. With less conversion of testosterone to oestradiol, the hypothalamic-pituitary axis receives corrected feedback signals, gonadotropin secretion normalises, and the testes resume adequate testosterone production.

Moreover, tirzepatide improves insulin sensitivity. Insulin resistance is independently associated with lower sex hormone-binding globulin (SHBG) and lower total testosterone. By improving metabolic health on multiple fronts, Mounjaro creates the conditions for hormonal recovery that diet alone often cannot achieve at the same speed or scale.

This matters clinically because unlike TRT, which replaces testosterone from an external source and suppresses the body’s own production, Mounjaro supports the restoration of natural hormone synthesis. For men who wish to preserve fertility, this distinction is particularly important, as TRT can significantly reduce sperm count.

Restoring testosterone to normal levels has wide-ranging benefits beyond sexual health. Men with adequate testosterone typically experience improved energy levels and reduced fatigue, better mood and lower rates of depressive symptoms, increased motivation for physical activity, greater capacity to build and preserve lean muscle mass during weight loss, reduced visceral fat accumulation, and improved cardiovascular risk markers.

For men tracking their body composition during Mounjaro treatment, DEXA London, CutKilo’s sister service at the same 86 Harley Street clinic, offers body composition scanning that can measure changes in lean mass, fat mass, and visceral fat independently. This is especially valuable for men concerned about whether they are losing fat or muscle during treatment.

In particular, the combination of rising testosterone and structured resistance exercise during Mounjaro treatment may help men preserve or even gain lean tissue while losing significant amounts of body fat. A DEXA scan before and during treatment provides objective data to guide training and nutrition decisions.

Not every man on Mounjaro will experience a meaningful testosterone increase. The greatest improvements are seen in men who have obesity-related (functional or metabolic) hypogonadism, meaning their low testosterone is driven primarily by excess body fat rather than a primary testicular or pituitary disorder.

Specifically, candidates most likely to benefit include men with a BMI above 30 and confirmed low total testosterone (below 12 nmol/L), men with symptoms of low testosterone such as fatigue, low libido, erectile difficulties, or loss of motivation alongside significant excess weight, and men who have been advised to consider TRT but would prefer to restore their own hormonal function naturally.

It is important to note that men with primary hypogonadism (where the testes themselves are damaged or dysfunctional, for instance due to Klinefelter syndrome or prior chemotherapy) will not recover testosterone through weight loss alone and still require specialist endocrine management.

Does Mounjaro directly increase testosterone? No. Tirzepatide does not act on the testes or testosterone-producing pathways directly. The testosterone increase occurs indirectly through substantial fat loss, which reduces aromatase activity and allows the hypothalamic-pituitary-gonadal axis to normalise.

Is Mounjaro better than TRT for low testosterone in obese men? The ENDO 2025 pilot study found that tirzepatide produced greater testosterone increases and better erectile function scores than transdermal TRT over two months in men with metabolic hypogonadism. Importantly, tirzepatide restored natural production while TRT suppressed it. However, larger and longer trials are needed before firm recommendations can be made.

Will my testosterone drop again if I stop Mounjaro? If you regain significant weight after stopping treatment, aromatase activity will increase again and testosterone may fall. Maintaining weight loss through diet, exercise, and ongoing medical support is essential for sustaining hormonal benefits.

Can I take Mounjaro and TRT together? Some men may benefit from both, particularly during the early stages of weight loss before natural testosterone has recovered. This should only be considered under the guidance of an endocrinologist or specialist doctor who can monitor hormone levels throughout treatment.

How long does it take for testosterone to improve on Mounjaro? The pilot study showed improvements within two months. The larger retrospective analysis showed progressive gains over 18 months. Generally, testosterone recovery tracks with fat loss and may take three to six months to become clinically significant.

For men with obesity-related low testosterone, Mounjaro offers something that TRT cannot: the restoration of the body’s own hormonal function rather than a lifelong external replacement. The emerging clinical evidence from ENDO 2025 and supporting studies suggests that tirzepatide-driven weight loss can break the vicious cycle of fat accumulation and testosterone suppression, with benefits extending to sexual health, energy, mood, and body composition.

This does not mean Mounjaro is a testosterone drug. It is a weight-loss and metabolic treatment that, by reducing the adipose tissue driving the hormonal problem, allows the male endocrine system to recover naturally. That distinction is clinically important and practically encouraging for the many men living with both obesity and low testosterone.