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Does Mounjaro increase oestrogen levels? This is a common question among patients prescribed tirzepatide for type 2 diabetes management. Mounjaro (tirzepatide) does not directly increase oestrogen production, as it works through dual incretin receptor activation to improve blood glucose control and facilitate weight loss. However, the significant weight reduction achieved with this medication can indirectly influence hormonal balance, including oestrogen levels. Understanding how Mounjaro affects metabolism, contraception, and reproductive hormones is essential for safe and effective treatment. This article examines the relationship between Mounjaro and oestrogen, addressing common concerns about hormonal changes during therapy.
Quick Answer: Mounjaro (tirzepatide) does not directly increase oestrogen levels but weight loss from the medication can indirectly affect hormonal balance.
Mounjaro (tirzepatide) does not directly increase oestrogen levels. This medication is a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist, primarily prescribed for type 2 diabetes management in the UK. The weight management formulation of tirzepatide is marketed as Zepbound in the UK. Mounjaro's mechanism of action focuses on improving blood glucose control through effects on insulin secretion, glucagon suppression, and appetite regulation.
There is no established link between Mounjaro and increased oestrogen production or secretion. The drug does not act on ovarian tissue, the adrenal glands, or other oestrogen-producing organs. However, weight loss achieved with Mounjaro can indirectly influence hormone levels, including oestrogen. Adipose (fat) tissue produces oestrogen through the conversion of androgens via the enzyme aromatase. When substantial fat loss occurs, this peripheral oestrogen production may decrease, potentially affecting overall hormonal balance.
Some patients have anecdotally reported changes in menstrual patterns whilst taking Mounjaro. These changes are more likely related to weight loss itself rather than direct drug action on oestrogen, though multiple factors may contribute. Rapid weight reduction can temporarily disrupt the hypothalamic-pituitary-ovarian axis, leading to irregular periods, changes in cycle length, or alterations in premenstrual symptoms. Additionally, improved insulin sensitivity—a key benefit of Mounjaro—may positively affect conditions like polycystic ovary syndrome (PCOS), where hormonal imbalances are common, though evidence specific to tirzepatide in PCOS remains limited.
Mounjaro exerts its therapeutic effects through dual incretin receptor activation, which has wide-ranging metabolic consequences beyond glucose control. The GIP and GLP-1 pathways influence insulin secretion from pancreatic beta cells, suppress inappropriate glucagon release, slow gastric emptying, and reduce appetite through central nervous system effects. These actions collectively improve glycaemic control and facilitate weight loss.
Weight loss is the primary driver of hormonal changes observed with tirzepatide therapy. In clinical trials, weight loss varied by population and indication—in type 2 diabetes trials, weight loss was generally more modest, while in weight management trials (as Zepbound), mean losses of up to 20-22% were observed at higher doses. As adipose tissue decreases, several metabolic improvements occur: insulin sensitivity increases, inflammatory markers decline, and sex hormone-binding globulin (SHBG) levels may rise. Higher SHBG levels can reduce the amount of free (biologically active) oestrogen and testosterone circulating in the bloodstream. For women with PCOS, these metabolic improvements may help restore more regular ovulation and menstrual cycles.
The medication may also influence leptin and adiponectin, hormones produced by fat cells that regulate energy balance and insulin sensitivity. As weight decreases, leptin levels typically fall (reducing the signal of energy abundance), whilst adiponectin often increases (improving metabolic health). These shifts can affect reproductive hormone regulation indirectly.
Thyroid function generally remains stable on Mounjaro. Rodent studies have shown C-cell tumours with GLP-1 receptor agonists, but the human relevance is unknown. Patients should report symptoms such as neck lumps, difficulty swallowing, or persistent hoarseness to their healthcare provider. Other important safety considerations include monitoring for signs of pancreatitis (severe abdominal pain), gallbladder disease, and hypoglycaemia risk when used with insulin or sulfonylureas.
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Oral contraceptive efficacy may be temporarily reduced when starting Mounjaro or increasing the dose, which is a critical consideration for women of childbearing age. This occurs because Mounjaro slows gastric emptying, potentially affecting the absorption of oral medications, including combined oral contraceptives and progestogen-only pills. The Medicines and Healthcare products Regulatory Agency (MHRA) and manufacturer guidance recommend that women using oral contraception should switch to a non-oral method or add barrier contraception for four weeks after initiating Mounjaro or escalating the dose.
Non-oral contraceptive methods are not affected by Mounjaro's mechanism of action. These include:
Intrauterine devices (IUDs) – both copper and hormonal (levonorgestrel-releasing)
Contraceptive implants (etonogestrel)
Injectable contraceptives (depot medroxyprogesterone acetate)
Contraceptive patches and vaginal rings
Barrier methods such as condoms
Vomiting and diarrhoea, which can occur as side effects of Mounjaro, may further reduce oral contraceptive reliability. Follow standard advice for missed pills if vomiting occurs within 3 hours of taking an oral contraceptive.
Women should not become pregnant whilst taking Mounjaro. The medication should be discontinued at least 1 month before a planned pregnancy, as there is insufficient data on its safety during pregnancy. The improved metabolic health achieved with Mounjaro may restore fertility in women with PCOS or obesity-related anovulation, sometimes unexpectedly. This makes reliable contraception particularly important during treatment.
For women taking hormone replacement therapy (HRT) for menopausal symptoms, there is no established evidence that Mounjaro interferes with HRT efficacy. While the same gastric emptying considerations could theoretically apply to oral HRT formulations, specific data are limited. Transdermal HRT (patches or gels) would not be affected by Mounjaro's gastrointestinal effects. Patients should discuss their individual circumstances with their GP or specialist.
Certain symptoms warrant prompt medical review whilst taking Mounjaro, particularly those that might indicate hormonal changes or complications. You should contact your GP or healthcare provider if you experience:
Significant menstrual irregularities – particularly if previously regular cycles become very irregular, absent for more than three months (in premenopausal women not on hormonal contraception), or if bleeding becomes unusually heavy
Unexpected pregnancy symptoms – especially if you've been relying on oral contraception, as reduced efficacy could lead to unintended pregnancy
Severe or persistent pelvic pain – which could indicate ovarian cysts or other gynaecological issues
New or worsening menopausal symptoms – such as severe hot flushes, night sweats, or mood changes
Severe abdominal pain – particularly if radiating to the back, which could indicate pancreatitis
Right upper abdominal pain or yellowing of skin/eyes – which might suggest gallbladder disease
Persistent vomiting or signs of dehydration – requiring prompt medical attention
Symptoms of low blood sugar – if taking Mounjaro with insulin or sulfonylureas
Neck lumps, difficulty swallowing, or persistent hoarseness – which should be evaluated
Before starting Mounjaro, discuss your complete medical and medication history with your prescriber, including current contraception, HRT, fertility plans, and any history of hormonal disorders such as PCOS, endometriosis, or thyroid disease. Baseline tests typically focus on diabetes-related parameters rather than routine hormonal assessments.
Regular follow-up is essential when taking Mounjaro. NICE guidance recommends reviewing response to treatment at around 6 months, assessing weight loss, glycaemic control, tolerability, and any concerns. This provides an opportunity to discuss any hormonal symptoms or menstrual changes you've noticed. If you're planning pregnancy, discuss discontinuation timing—at least 1 month before attempting to conceive. Report any suspected side effects via the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk). Your healthcare team can provide personalised advice based on your individual circumstances.
Yes, some patients report menstrual changes whilst taking Mounjaro, typically due to weight loss affecting the hypothalamic-pituitary-ovarian axis rather than direct drug effects on hormones. Significant irregularities should be discussed with your GP.
If you use oral contraception, you should switch to a non-oral method or add barrier contraception for four weeks after starting Mounjaro or increasing the dose, as delayed gastric emptying may reduce oral contraceptive absorption.
There is no established evidence that Mounjaro interferes with HRT efficacy, though transdermal HRT (patches or gels) would not be affected by the medication's gastrointestinal effects. Discuss your individual circumstances with your GP.
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DisclaimerThis content is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional with any medical questions or concerns. Use of the information is at your own risk, and we are not responsible for any consequences resulting from its use.
