Underactive thyroid: why fatigue and weight gain are not a diagnosis

An underactive thyroid can gradually cause fatigue, cold sensitivity, constipation and weight gain, but these symptoms overlap with other conditions. Diagnosis requires assessment and thyroid blood tests rather than a checklist alone.

Treatment replaces missing hormone, with follow-up tests guiding the dose. Feeling better is not a reason to alter medication yourself; persistent fatigue also needs discussion rather than an unsupervised increase.

Tell your clinician when planning pregnancy or becoming pregnant, because testing and treatment adjustments may be needed. Monitoring supports a healthy pregnancy rather than simply renewing an old prescription.