Thyroid hormone replacement: what to know and how to use it

Feeling unusually tired, cold, or slow? Those are classic signs of low thyroid function. Thyroid hormone replacement is the main treatment for hypothyroidism and it works well for most people — when the drug, dose, and monitoring are right. This short guide gives clear, practical advice so you can talk with your doctor and avoid common mistakes.

Which medicines are used?

There are three main options. Levothyroxine (T4) is the most common: it converts in your body to the active hormone and has a long, steady effect. Liothyronine (T3) acts faster and is sometimes added for people who still have symptoms on T4 alone. Desiccated thyroid is made from animal thyroids and contains both T4 and T3 — some people feel better on it, but doses are less predictable. Your doctor may use a combination depending on symptoms, lab results, and personal preference.

Brands and formulations can vary in price and absorption. If you switch brands or pharmacies, tell your clinician so blood levels can be rechecked.

How to take it and what blocks absorption

Take thyroid hormone on an empty stomach for consistent absorption — usually 30 to 60 minutes before breakfast or at least 3–4 hours after the last meal if taken at night. Avoid calcium, iron, antacids, and some supplements within four hours of the dose. Coffee and some high-fiber foods can reduce absorption if you take your pill right before eating.

Certain drugs (like proton-pump inhibitors, some antiepileptics, and calcium channel blockers) and gut conditions (celiac disease, bacterial overgrowth) can change how much hormone your body gets. If you start or stop other meds, plan for a dose check.

Missed a single dose? Take it as soon as you remember unless it's near your next dose. Never double up regularly without medical advice.

Older adults and people with heart disease usually start at lower doses. Pregnant people need higher doses and tighter monitoring — tell your doctor if pregnancy is planned or confirmed.

Monitoring is simple but essential. TSH (and sometimes free T4) checks are done about 6–8 weeks after a dose change, then less often once stable. Feeling better doesn’t always mean labs are optimal, and normal labs don’t always mean you feel perfect — both matter.

Watch for signs of under-replacement (fatigue, weight gain, cold intolerance, constipation) and over-replacement (palpitations, weight loss, tremor, anxiety, bone loss). If you notice new symptoms, get blood tests before changing doses yourself.

Buying tips: always use a licensed pharmacy and keep your prescription current. Shop around for price comparisons, but avoid sites that don’t require a prescription. Cost matters, but safety does too.

Want a quick checklist to bring to your next appointment? Note your current dose, symptoms, other meds/supplements, pregnancy plans, and any recent brand changes. That list makes dose decisions faster and safer.