Effects of Tirzepatide, Metformin, and Erenumab on Menstrual Periods and UTI Risk
Metformin can normalize irregular menstrual cycles in women with polycystic ovary syndrome (PCOS) or insulin resistance, potentially causing changes in menstrual timing, while tirzepatide and erenumab (Amovig) do not have established effects on menstrual periods, and none of these medications are known to cause urinary tract infections.
Metformin and Menstrual Effects
Metformin's impact on menstruation depends entirely on your underlying metabolic status:
- In women with PCOS or insulin resistance, metformin improves menstrual cyclicity by enhancing insulin sensitivity and normalizing hormonal imbalances 1, 2.
- Studies demonstrate that 95.7% of oligoamenorrheic women with PCOS achieved restoration of menstrual cyclicity after 6 months of metformin therapy 3.
- Metformin can cause unexpected vaginal bleeding in some women, particularly if endometrial hyperplasia is present, as the medication's endocrine effects may trigger sloughing of hyperplastic tissue 4.
Key Clinical Caveat
- If you experience new or abnormal vaginal bleeding after starting metformin, this warrants medical evaluation to exclude endometrial disease 4.
- The first step for any missed or delayed period is always a pregnancy test, as metformin enhances fertility in women with insulin resistance or PCOS 1.
Tirzepatide and Menstrual Effects
- Tirzepatide is a dual GIP/GLP-1 receptor agonist approved for type 2 diabetes management 5, 6.
- There is no established evidence that tirzepatide directly affects menstrual cycle timing or delays periods 5, 6.
- The most common adverse events are gastrointestinal (nausea 17-22%, diarrhea 13-16%, vomiting 6-10%) 6.
- Like metformin, tirzepatide causes weight loss (mean reductions of 1.9-5.5 kg more than semaglutide), and significant weight changes can indirectly affect menstrual regularity through metabolic effects 5, 6.
Erenumab (Amovig) and Menstrual Effects
- Erenumab is a CGRP receptor antagonist used for migraine prevention.
- There is no documented evidence linking erenumab to menstrual cycle changes or delays based on available clinical data.
- Menstrual irregularities are not listed among the known adverse effects of this medication.
Urinary Tract Infection Risk
None of these three medications—tirzepatide, metformin, or erenumab—are known to increase the risk of urinary tract infections:
- Metformin's primary side effects are gastrointestinal (bloating, abdominal discomfort, diarrhea) 5.
- Tirzepatide's adverse events are predominantly gastrointestinal 6.
- UTIs are not documented as adverse effects for any of these medications.
Important Consideration
- If you are experiencing UTI symptoms, this represents a separate medical issue requiring evaluation and treatment independent of these medications.
- The American Diabetes Association recommends that drugs affecting cycle regularity, hormones, or fertility signs should be carefully evaluated, and barrier contraception should be offered until the degree of effect is determined 5.
Clinical Bottom Line
- Metformin is the only medication among these three that can affect menstrual timing, but only in women with underlying insulin resistance or PCOS, where it typically normalizes rather than delays periods 1, 2, 3.
- In women without PCOS or insulin resistance, metformin should not affect menstrual cycles 7.
- Any new menstrual irregularity after starting these medications warrants pregnancy testing first, followed by medical evaluation if bleeding patterns are abnormal 1, 4.