Mounjaro (tirzepatide) is licensed in the UK for weight management. [1] In studies of men with obesity, testosterone rose during treatment with tirzepatide and similar medicines, and the rise tracked the weight lost. [2] [3] [4] A 2026 review judges the rise largely a result of the weight loss and improved insulin sensitivity rather than a direct hormonal action. [4]

None of the studies cited here found a fall in testosterone. Tirzepatide is a GIP and GLP-1 receptor agonist: a medicine that acts on the receptors for two gut hormones that regulate appetite. [1] Medicines in this group are called incretin medicines.

This article is education. HeMed’s blood test does not measure testosterone. The hormone tests belong with your GP.

Does Mounjaro affect testosterone? The short answer

Indirectly, on the evidence so far. In men with obesity, testosterone tends to rise as weight falls, and that is what the tirzepatide studies show. [2] [3] [4] In these studies the change tracked the weight lost: the more weight lost, the larger the average rise. [2]

Can Mounjaro affect testosterone the other way? None of the studies cited here found a fall, and the licence lists no effect on testosterone. [1]

Research on the effect of Mounjaro on testosterone covers men with obesity, most of them with low testosterone or type 2 diabetes. [2] [3] It says nothing about men with normal weight.

Why do men with obesity often have low testosterone?

Fat tissue carries aromatase, an enzyme that converts testosterone into oestradiol, a form of oestrogen. [6] One explanation is that excess fat raises aromatase activity and oestradiol, which feeds back to suppress the hypothalamic-pituitary-gonadal axis. [7] [6] The European guideline calls this a hypothesis. [7]

That axis is the signalling chain from the brain to the testes, and inflammatory signals from fat tissue can suppress it too. [7] The body’s cells can also respond less well to the hormone insulin, which is called insulin resistance. It lowers SHBG, the protein that carries testosterone in the blood, and so lowers total testosterone further. [6]

In a US study of 1,849 men aged 45 and over, 40% of men with obesity and no diabetes had subnormal free testosterone. [5] Free testosterone is the part not bound to proteins in the blood. Among men with obesity and diabetes the figure was 50%. [5]

Doctors call this metabolic hypogonadism, or functional hypogonadism: low testosterone with normal or low pituitary signals and no disease of the testes or pituitary. [3] It is functional and not permanent, and it can reverse with substantial weight loss. [6] Our article on low testosterone and weight gain explains the cycle in full.

What happens to testosterone when men lose weight on tirzepatide?

Total testosterone rose in all three kinds of evidence: a health-record study of 215 men, a 2-month pilot study and a review of 29 studies. [2] [3] [4] All three have limits. Testosterone is reported in two units here: 1 nmol/L is about 28.8 ng/dL.

The 215-man health-record study

Researchers at a US hospital reviewed the records of men aged 18 to 89 who were prescribed incretin weight-loss medicines. [2] The records ran from 2021 to 2024. [2] The paper’s abstract does not name the medicines one by one; the same group’s earlier conference report listed tirzepatide among them. [2] [8]

The 215 men had a mean BMI of 36.3, and 77% had type 2 diabetes. [2] BMI is body mass index, a measure of weight relative to height.

Mean total testosterone rose from 332 to 399 ng/dL, about 11.5 to 13.8 nmol/L, with around 5% weight loss. [2] The share of men with a normal total testosterone rose from 67% to 86%. [2] The men who lost most weight had the largest rises. [2]

The study was retrospective, meaning it looked back at records, and it had no control group of men who were not on the medicines. [2] It shows what happened to the men in it. It cannot show that the medicine caused the change.

The same group presented earlier results from 110 men at the Endocrine Society’s 2025 meeting. [8] Those conference figures are the ones most health coverage carries. [9] [10] [11] The published paper supersedes them.

The 2-month pilot study

An Italian team studied 83 men aged 44 to 63 with obesity and metabolic hypogonadism. [3] Their BMI was 30 to 39.9 and their total testosterone was below 12 nmol/L, about 346 ng/dL. [3]

In the study, 28 men took tirzepatide with a reduced-calorie diet and a daily walk. Another 30 made the lifestyle changes alone, and 25 had testosterone therapy with the lifestyle changes. [3]

The men were not randomised, meaning they were not assigned to a group by chance. Cost and preference shaped who took what. [3]

What the pilot found

After 2 months the tirzepatide group had lost 8.1% of body weight. [3] Their median total testosterone rose from 186.5 to 424 ng/dL, about 6.5 to 14.7 nmol/L. [3] Their LH and FSH, the pituitary signals to the testes, rose, and their oestradiol fell. [3]

In the lifestyle-only group, median total testosterone rose from 192 to 266 ng/dL, about 6.7 to 9.2 nmol/L. [3]

Erectile function scores rose more in the tirzepatide group than with lifestyle alone, but not more than with testosterone therapy. [3] The paper does not print the final scores. [3] That is a research signal in 83 men over 2 months, not a treatment claim.

The authors list the limits themselves: a small sample, a 2-month duration, no randomisation and no comparison with other obesity medicines. [3] The study received no funding and the authors declared no competing interests. [3]

What the review of 29 studies concludes

A systematic review gathers every published study on a question. A 2026 review found 29 studies of incretin medicines in men with hypogonadism. [4]

Across the included studies, mean total testosterone rose by 2.5 to 5.2 nmol/L, about 72 to 150 ng/dL, in men with obesity-related functional hypogonadism. [4] The range covers several incretin medicines, not tirzepatide alone. [4]

The authors judged the effect “largely mediated by weight loss and improvement of insulin resistance”. [4]

They also describe a possible direct action of these medicines on the hormone axis. [4] Only randomised trials with weight-stable comparison groups could separate the two, they say. [4] They rated the risk of bias in the studies moderate to high. [4]

Why weight loss is the likely reason

In studies of men with obesity, weight loss by diet or surgery has raised testosterone. [12] A meta-analysis pools the results of many studies.

A meta-analysis of 24 weight-loss studies found total testosterone rose by 2.87 nmol/L with a low-calorie diet and by 8.73 nmol/L after bariatric (weight-loss) surgery. [12] The amount of weight lost was the best predictor of the rise. [12]

In men with obesity-related low testosterone, a low-calorie diet can raise testosterone, reduce oestrogens and restore normal pituitary signals. [7] The European urology guideline adds that the rise from diet and exercise alone is small, 1 to 2 nmol/L. [7] In the tirzepatide studies the rise also tracked the weight lost. [2] [4]

Men often ask: does Mounjaro increase testosterone directly? No study cited here can separate a direct effect from the weight loss. The reviewers judge the change largely mediated by weight loss and improved insulin resistance. [4]

What the studies cannot tell you

  • None of the studies cited here is a placebo-controlled trial. A placebo is a dummy treatment used for comparison.
  • The health-record study was retrospective, and 77% of its men had type 2 diabetes. [2]
  • The pilot lasted 2 months and was not randomised. [3]
  • Neither the health-record study nor the pilot followed men after they stopped treatment. [2] [3]
  • The two primary studies were run in the US and Italy, not the UK. [2] [3]

Average results describe groups, not any one man.

Does Mounjaro lower testosterone?

None of the studies cited here found a fall in testosterone on tirzepatide. [2] [3] [4] The Mounjaro licence lists no effect on testosterone: the word does not appear anywhere in its Summary of Product Characteristics (SmPC), the licence document. [1]

The men’s health press has asked the same question: does it raise or lower testosterone? [13] In men with obesity, the evidence so far points to a rise. Two cautions apply.

First, the studies cover men with obesity, most of them with low testosterone or type 2 diabetes. [2] [3] They say nothing about men with normal weight or normal testosterone.

Second, testosterone that is low and stays low after weight loss needs a GP review. It is not a reason to change your weight-loss medicine on your own.

Mounjaro and testosterone replacement therapy (TRT)

Testosterone replacement therapy (TRT) is prescribed testosterone for men with a confirmed deficiency. [14] HeMed does not prescribe or monitor testosterone. This section is information for men who take it or are considering it.

Can you take Mounjaro and testosterone together?

The Mounjaro licence lists no interaction with testosterone. [1] Its interactions section covers oral medicines. [1] Tirzepatide delays stomach emptying and can slow their absorption. [1]

The licence gives specific advice on oral contraceptives. [1] No study cited here tested the two together: the pilot gave tirzepatide and testosterone therapy to separate groups. [3]

The licence does not mention testosterone, and no study cited here has looked at the two together. If you take testosterone, tell the clinician who prescribes your weight-loss medicine. Tell the clinician who prescribes your testosterone too.

Each needs the full list of your medicines, and the decision is theirs. The same applies whether you are considering Mounjaro with testosterone already prescribed, or testosterone and Mounjaro together from the start.

In one news report on the health-record study, a researcher said men already on testosterone therapy should monitor their levels closely after starting weight-loss medicines. [11] That is a researcher’s view as reported, not a licence instruction. Your prescribers decide what monitoring you need.

Weight loss or testosterone therapy first: what the guidelines say

The European Association of Urology’s guideline recommends improving lifestyle and reducing weight before starting testosterone therapy, a strong recommendation. [7] It calls weight loss and lifestyle change the first approach for all men with low testosterone who are overweight or have obesity. [7]

The British Society for Sexual Medicine’s 2023 guideline calls weight reduction and lifestyle change important first steps, but takes a different emphasis. [14] In men with symptoms and a confirmed deficiency, it recommends lifestyle change together with testosterone therapy. [14] It does not support lifestyle change alone as first-line treatment. [14]

The pilot study is not a basis for choosing between the two routes. It was small, short and not randomised, and the men chose their groups rather than being assigned by chance. [3]

A decision for an individual man rests with his GP or endocrinologist, a hormone specialist, after repeat morning blood tests. [14] The condition summary on low testosterone in men sets out the NHS route.

Should you get your testosterone tested first?

If you have symptoms of low testosterone, ask your GP for a morning testosterone test. The NHS lists these features of late-onset hypogonadism: [15]

  • reduced sex drive
  • erection problems
  • low mood or irritability
  • loss of muscle mass and strength
  • increased body fat
  • tiredness
  • poor concentration

In many men with these symptoms the cause is not hormonal. [15]

Diagnosis needs symptoms plus a low result on a morning sample taken between 7 and 11 am, measured on at least two occasions. [14] HeMed’s blood test does not measure testosterone, SHBG, LH or FSH. The hormone tests belong with your GP, who can arrange them.

If your results stay low after you have lost weight, the NHS route is a GP review. Where deficiency is confirmed, the GP refers you to an endocrinologist. [15]

Weight loss and hormone testing are not either-or. Both can run at once, with each clinician told about the other.

How does HeMed fit in?

HeMed starts with a blood test. We measure 10 metabolic markers across four systems from a needle-free blood test at home. Testosterone is not one of the markers.

A clinician reviews your blood test first. If they approve treatment, we deliver it the next working day, discreetly packaged, with delivery included in your plan.

A weekly in-app check-in, reviewed by clinicians, so your plan can be adjusted when it needs to be. A retest every 6 months shows what’s actually changing.

Mounjaro is a prescription medicine for weight management. Whether it’s right for you is a clinical decision, made from your health information and your baseline blood test.

Frequently asked questions

Can you take Mounjaro while on testosterone?

The Mounjaro licence does not mention testosterone, and no study cited here has looked at the two together.

Tell the clinician who prescribes your weight-loss medicine that you take testosterone, and tell your testosterone prescriber about the weight-loss medicine. The decision sits with them.

Does Mounjaro reduce testosterone?

None of the studies cited here found a fall in testosterone on tirzepatide, and the licence lists no effect on the hormone. In men with obesity the studies found a rise that tracked the weight lost.

The evidence comes from men with obesity, most with low testosterone or type 2 diabetes. It does not cover men with normal weight or normal testosterone.

How long before testosterone changes on treatment?

Two of the studies cited here report when they measured. The pilot study measured testosterone after 2 months of tirzepatide. [3] The health-record study measured it before and during treatment, in records running from 2021 to 2024. [2]

Neither tells you when a change starts for an individual. In both, the rise tracked the weight lost. [2] [3]

Will testosterone fall again if you stop treatment?

Neither the health-record study nor the pilot followed men after stopping, so there is no measured answer. What they show is that the rise in testosterone tracked the weight lost. [2]

Talk to your clinician before stopping any prescribed medicine.

Does the evidence cover libido or erections?

Libido was not measured. The pilot study measured erectile function: scores rose more in the tirzepatide group than with lifestyle alone, but not more than with testosterone therapy. [3] The paper does not print the final scores. [3]

That is a research signal in 83 men over 2 months, not a treatment claim. Erection problems have several possible causes. They are a reason to see your GP, whatever your weight.

Can you get testosterone checked through HeMed?

No. HeMed’s blood test does not measure testosterone or the related hormones. Ask your GP for a morning testosterone test if the symptoms above sound familiar.

HeMed’s 10 markers cover the metabolic picture around it. They include cholesterol, triglycerides (a blood fat), liver enzymes, HbA1c (your average blood sugar over roughly 3 months) and TSH (thyroid-stimulating hormone). A clinician reviews every result.

HeMed provides clinician-led weight management and does not diagnose or treat low testosterone. Treatment is prescription-only and is prescribed only where a clinician decides it is suitable. This page is general health information, not medical advice: if you are worried about symptoms, speak to your GP, or use NHS 111.

Next step: read the Mounjaro (tirzepatide) information page.

Sources (15)
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  2. Portillo-Canales S, Iqbal I, Akande R, Ghimire A, Kalishman A, Wood E, Albert SG, Dhindsa S, “Effect of incretin-based weight loss drugs on testosterone concentrations in men”, Endocrine Practice 2026;32(5):696 to 703. doi.org/10.1016/j.eprac.2026.01.003. Accessed 6 November 2026.
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  6. Fui MN, Dupuis P, Grossmann M, “Lowered testosterone in male obesity: mechanisms, morbidity and management”, Asian Journal of Andrology 2014;16(2):223 to 231. doi.org/10.4103/1008-682X.122365. Accessed 6 November 2026.
  7. European Association of Urology, “EAU guidelines on sexual and reproductive health”, 2026 edition (a limited update of the 2025 publication), chapter 3, male hypogonadism, sections 3.3, 3.4.3.a and 3.4.3.c. uroweb.org/guidelines/sexual-and-reproductive-health/chapter/male-hypogonadism. Accessed 6 November 2026.
  8. Endocrine Society, “Anti-obesity medications can normalize testosterone levels in men”, ENDO 2025 press release, 14 July 2025. endocrine.org. Accessed 6 November 2026.
  9. Mammoser G, “GLP-1 drugs may boost testosterone levels in men with obesity, diabetes”, Healthline, 16 July 2025. healthline.com/health-news/glp-1-drugs-may-improve-low-testosterone. Accessed 6 November 2026.
  10. Ferruggia K, “GLP-1 medications can increase testosterone levels in men with obesity”, Pharmacy Times, 21 July 2025. pharmacytimes.com. Accessed 6 November 2026.
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Numbered markers in the page text link to these entries. Statistics describe populations, not any one person’s results.

Published 6 November 2026.