Thyroid hormones: what T3 and T4 do — and how to manage them

Do you feel tired, cold, or notice sudden weight changes? Those vague symptoms can point to a thyroid problem. The thyroid makes two main hormones — T4 (inactive) and T3 (active). Together they control your energy, temperature, heart rate, and metabolism. Knowing what they do helps you make smart choices about testing and treatment.

How thyroid hormones work and common tests

Your body releases T4 from the thyroid gland, and the liver and other tissues convert some of it to T3. Doctors usually check TSH first — that’s the pituitary signal telling your thyroid to work. If TSH is off, labs may measure free T4 and sometimes free T3. High TSH plus low T4 usually means underactive thyroid (hypothyroidism). Low TSH with high T4/T3 points to an overactive gland (hyperthyroidism).

Tests can change with illness, pregnancy, or certain meds. Bring a list of medications to your appointment — things like steroids, amiodarone, or biotin can skew results. If you’re on treatment, regular blood checks help keep doses steady: often every 6–12 weeks when starting or changing dose, then every 6–12 months once stable.

Treatment options, monitoring, and safe buying tips

Most people with low thyroid function take levothyroxine, a synthetic T4. It’s usually once daily and works well for many. Some people still feel unwell on T4 alone and may discuss adding liothyronine (T3) or trying desiccated thyroid — those are options your doctor may consider. Read our site articles “Exploring Alternatives to Synthroid for Thyroid Health” and “Affordable Thyroid Treatments” for comparisons of generics, brands, and natural choices.

Dosing is personal. Your doctor aims for a TSH in a target range tailored to your age and health. Don’t change dose on your own. If symptoms persist despite normal labs, ask about checking free T3, reverse T3, antibodies for autoimmune thyroiditis, or assessing other causes like anemia or depression.

Medication timing matters: take levothyroxine on an empty stomach, 30–60 minutes before breakfast, and avoid calcium or iron within four hours. If you take other meds, separate them to prevent absorption problems.

Thinking of buying thyroid meds online? Be careful. Look for licensed pharmacies, clear contact info, and a valid prescription policy. Our guides about safer online pharmacies explain what red flags to watch for — fake pills, lack of pharmacist access, or prices that seem too good to be true.

If you suspect thyroid problems, get tested and talk with a clinician before trying supplements or switching meds. Small lab shifts are normal, but patterns plus symptoms guide smart, safe care. For step-by-step help, check the linked articles on HeyDoctor.com to compare options and learn practical tips for tests, dosing, and affordable choices.