Constipation
Constipation — infrequent, hard or difficult bowel movements — is common and has many causes. Hypothyroidism is a recognised contributor because thyroid hormone affects gut motility.
It is a non-specific symptom that only suggests thyroid testing when combined with other features.
Last medically reviewed: 1 November 2025
Thyroid connection
Hypothyroidism slows intestinal motility, contributing to constipation alongside fatigue, weight gain and cold intolerance. It is a classic but non-specific feature.
Hyperthyroidism more often causes loose stools or diarrhoea — the opposite pattern.
Other causes
Low fibre or fluid intake, sedentary lifestyle, medications (opioids, iron, some antidepressants, calcium channel blockers), pregnancy, hypothyroidism, diabetes affecting nerves, pelvic floor problems, and irritable bowel syndrome all cause constipation.
In many cases, simple dietary and lifestyle factors are responsible.
Evaluation
Thyroid testing is reasonable when constipation is accompanied by other hypothyroid features or is new and unexplained. Alarm features — blood in stool, weight loss, severe pain, change in bowel habit in older adults — need prompt evaluation regardless.
Persistent constipation despite lifestyle measures warrants medical review.
Frequently asked questions
Can levothyroxine cause constipation?
Rarely — under-replacement can worsen constipation; correct dosing typically improves it. If constipation persists on adequate treatment, other causes should be sought.
Does hyperthyroidism cause diarrhoea?
Yes — increased gut motility can cause loose stools or diarrhoea, the opposite of hypothyroidism.
When should constipation worry me?
New constipation with blood, weight loss, severe pain, or in older adults with changed bowel habits needs prompt assessment.
References & further reading
This page is based on established medical knowledge and guidelines from authoritative sources. Always consult a qualified clinician for personal medical advice.
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