Can Hyperthyroidism Cause Heavy Menstrual Bleeding?
Hyperthyroidism rarely causes heavy menstrual bleeding; it more commonly causes decreased menstrual flow (oligomenorrhea) or absent periods, though increased bleeding can occasionally occur.
Understanding the Menstrual Pattern in Hyperthyroidism
The relationship between hyperthyroidism and menstruation is well-established but often misunderstood:
The typical pattern is reduced bleeding, not increased bleeding. Oligomenorrhea (decreased menstrual flow) is the most common manifestation in hyperthyroidism 1, 2.
Heavy bleeding is rare in hyperthyroidism. While increased bleeding may occur, it is explicitly described as uncommon 1, 2.
Modern diagnosis has changed the clinical picture. Because hyperthyroidism is now diagnosed earlier than historically, the clinical presentation is generally milder, and menstrual disorders are less common than in older case series 3.
Evidence from Recent Studies
Contemporary research confirms this pattern:
In a study of 214 thyrotoxic patients, only 21.5% had any menstrual disturbances, compared to historical reports of 50% 3.
No patients presented with amenorrhea in this modern cohort, and the study found that hyperthyroidism is less frequently associated with menstrual abnormalities than previously believed 3.
A 2024 study found that the types and frequencies of menstrual disorders in patients with hyperthyroidism were not significantly different from controls 4.
When to Suspect Thyroid Disease in Heavy Bleeding
According to guideline-based evaluation of abnormal uterine bleeding:
Thyroid-stimulating hormone (TSH) and prolactin levels should be measured as part of the diagnostic workup for abnormal uterine bleeding 5, 6.
The PALM-COEIN classification system includes ovulatory dysfunction (which can be caused by thyroid disease) as a non-structural cause of abnormal bleeding 5, 6.
Thyroid disease is listed as a cause of anovulation that should be considered during evaluation of abnormal uterine bleeding 5.
Clinical Implications
If a patient presents with both hyperthyroidism and heavy menstrual bleeding:
Look for alternative causes first. The heavy bleeding is more likely due to another etiology in the PALM-COEIN classification (polyps, adenomyosis, leiomyomas, coagulopathy, endometrial disorders) 5, 6.
Anovulatory cycles are very common in hyperthyroidism and could contribute to irregular bleeding patterns 1, 2.
Smoking and higher T4 levels are associated with menstrual disturbances in thyrotoxicosis, with smokers having significantly higher rates of irregular periods (50% vs 19%) 3.
Contrast with Hypothyroidism
It's important to distinguish hyperthyroidism from hypothyroidism:
Hypothyroidism causes the opposite pattern: polymenorrhea (increased menstrual bleeding) and menorrhagia are more common 1, 2, 7.
In a 2024 study, hypermenorrhea was significantly more common in overt hypothyroidism (33%) compared to controls (6%), while hyperthyroidism showed no significant difference 4.
Defects in hemostasis may contribute to increased bleeding in hypothyroidism 1.