How can i know if i have an underactive thyroid?

Labs: You need to have TSH and free thyroxine or total thyroxine levels measured in your blood.

Tests and Symptoms: Symptoms of low thyroid function are commonly fatigue, weight gain, heavy periods (females), dry skin, hair thinning and loss, depression and constipation. Tsh, free T3 (liothyronine) and free T4 (if TSH is borderline) as well as some other older tests like morning baseline temperature and tendon reflex testing can all detect low thyroid function.

Blood test: You MAY feel sluggish, gain weight, have hair thin or fall out, feel a fullness in the front of your throat. These are all late findings and pretty inaccurate. Best to check with a doctor who can order some blood tests and find out much more accurately

Thyroid lab tests : Low thyroid function causes low energy, constipation, loss of hair, weight pain, puffy face, muscle pain, irregular menstrual periods