Reviewed by Dr. Arjun Mehta, PharmD — Head Pharmacist. Updated May 2025.
Women lifetime risk
Replacement dose
Time to retest
The thyroid gland sits at the base of the neck and produces hormones (T3 and T4) that regulate metabolism. Hypothyroidism (underactive thyroid) is the more common problem, especially in women and after age 40. Hyperthyroidism (overactive) is less common but more dramatic in presentation.
Hypothyroidism is treated by replacing the missing hormone with daily levothyroxine, taken on an empty stomach. Dose is titrated to TSH blood levels, and most patients need treatment for life. Hyperthyroidism is treated with carbimazole or methimazole (anti-thyroid drugs), radioactive iodine, or surgery.
Synthetic T4, the standard treatment for hypothyroidism. Take 30–60 min before food. Lifelong for most patients.
Synthetic T3. Faster-acting; used selectively in patients who don’t respond to T4 alone.
Anti-thyroid drug for hyperthyroidism. Slows hormone production. Specialist supervision.
Propranolol controls symptoms (tremor, palpitations, anxiety) of hyperthyroidism while definitive treatment takes effect.
A blood test showing raised TSH and low free T4. Symptoms — fatigue, weight gain, cold intolerance — are common but non-specific.
Switch carefully — different brands can differ slightly in absorption. Re-check TSH 6 weeks after any brand change.
Calcium, iron, soy and coffee all reduce absorption. Take levothyroxine at least 30–60 minutes before food or drinks other than water.

/our-pharmacists/arjun-mehta/ — Reviewed May 2025
This guide is reviewed every 12 months or sooner when clinical guidance changes. If you have a specific medical question, call our pharmacist team — we answer the phone, not a bot.