Hypothyroidism is treated by replacing the thyroid hormone your body isn’t making enough of. The standard approach is a daily pill called levothyroxine, a synthetic version of the hormone your thyroid would normally produce. Most people start feeling better within one to two weeks of beginning treatment, though finding the right dose can take a few months of fine-tuning.
How Thyroid Hormone Replacement Works
Your thyroid gland produces a hormone called T4, which your body converts into its active form, T3. Together, these hormones regulate your metabolism, energy levels, body temperature, heart rate, and dozens of other processes. When your thyroid can’t keep up, every system that depends on these hormones slows down. That’s why hypothyroidism can cause such a wide range of symptoms, from fatigue and weight gain to dry skin and brain fog.
Levothyroxine is a synthetic copy of T4. Once you take it, your body handles it the same way it would handle T4 from your own thyroid, converting it into T3 as needed. The goal is to bring your hormone levels back to normal so your body functions the way it should. Every major medical society, including the Endocrine Society, the American Thyroid Association, and the American Association of Clinical Endocrinologists, recommends synthetic levothyroxine as the preferred treatment.
Starting Dose and Adjustments
Your initial dose is typically calculated based on your body weight. Current guidelines recommend about 1.6 micrograms per kilogram of body weight per day, based on ideal or lean body mass rather than actual weight. For someone who is overweight, dosing by actual weight can lead to taking too much. People over 60 or those with heart conditions usually start at a lower dose and increase gradually.
After you begin treatment, your provider will check your TSH (thyroid-stimulating hormone) level about six to eight weeks later. TSH is the signal your brain sends to your thyroid telling it to make more hormone. When your thyroid hormone levels are too low, TSH rises. When replacement therapy brings your hormones back to normal, TSH drops back into the target range of 0.4 to 4 mIU/L. Based on that blood test, your dose gets adjusted up or down, and the process repeats until your levels stabilize.
What to Expect After Starting Treatment
Most people notice some improvement within the first week or two. Energy levels tend to pick up first, followed by gradual improvements in mood, mental clarity, and other symptoms over several weeks. Don’t expect everything to resolve at once. Some symptoms, like dry skin or hair changes, can take months to fully improve because they depend on slower biological cycles like hair growth.
Finding the right dose isn’t always a straight line. You may need two or three adjustments before your TSH settles into range and your symptoms resolve. Once you’re stable, your provider will typically recheck your levels once or twice a year, or sooner if your weight changes significantly, you become pregnant, or your symptoms return.
How to Take Levothyroxine Correctly
This medication is surprisingly sensitive to how and when you take it. Levothyroxine is best absorbed on an empty stomach, so the standard recommendation is to take it 30 to 60 minutes before eating. Most people take it first thing in the morning with a glass of water, then wait at least half an hour before breakfast or coffee.
Calcium supplements, iron supplements, and certain foods can block absorption if taken at the same time. If you take any of these, space them at least four hours apart from your levothyroxine. Consistency matters too. Taking it at roughly the same time each day, in the same way, helps keep your hormone levels steady and makes dose adjustments more reliable.
Risks of Too Much Thyroid Hormone
Getting the dose right isn’t just about feeling better. Taking more levothyroxine than your body needs pushes you into overtreatment, which carries its own health risks. The two most significant concerns are heart rhythm disturbances and bone loss. Excess thyroid hormone speeds up your heart rate and can trigger arrhythmias, particularly in people who already have heart conditions. It also accelerates bone turnover, increasing the risk of osteoporosis and fractures over time.
Elderly people and those with existing heart rhythm problems are most vulnerable to these complications. This is one reason providers start with lower doses in older patients and why regular blood monitoring continues even after you feel well. If your TSH drops below the normal range, it’s a signal that your dose may be too high, even if you feel fine.
When Mild Hypothyroidism Doesn’t Need Treatment
Not everyone with an abnormal thyroid test needs medication right away. Subclinical hypothyroidism, where TSH is mildly elevated (between 5 and 10 mIU/L) but T4 levels are still normal, is a gray area. Many people in this range have no symptoms at all.
Providers often recommend rechecking TSH within three months before starting any treatment, since levels can fluctuate. Treatment is more likely to be recommended when TSH is 10 mIU/L or higher, when symptoms are present in younger or middle-aged adults, or when other risk factors exist. Women undergoing fertility treatments like IVF are often treated to bring TSH below 2.5 mIU/L, since even mildly low thyroid function can affect pregnancy outcomes.
Combination Therapy and Natural Thyroid
Some people on levothyroxine still feel tired, foggy, or generally unwell despite normal blood tests. This has led to interest in two alternatives: adding a small dose of synthetic T3 to standard T4 therapy, or switching to desiccated thyroid extract (dried pig thyroid gland, sold under brand names like Armour Thyroid and NP Thyroid).
Combination T4/T3 therapy has been studied in patients with persistent symptoms. In one long-term study, 82% of patients who started combination treatment chose to stay on it, and those who responded well reported quality of life comparable to the general population. However, the picture is complicated. Even among responders, symptom scores remained high, similar to those seen in people with untreated hypothyroidism. And 38% of the responder group had TSH levels below 0.4 mIU/L, a sign of overtreatment that carries the bone and heart risks described above.
Desiccated thyroid extract contains both T4 and T3, but these products are not FDA-approved. The FDA notes that because of their complex biological origin, they contain many compounds that haven’t been fully characterized for safety and effectiveness. Despite this, an estimated 1.5 million patients in the U.S. received prescriptions for these medications from outpatient pharmacies in 2024. Professional guidelines continue to recommend synthetic levothyroxine as the preferred option, though some providers will prescribe desiccated thyroid for patients who prefer it or haven’t done well on standard therapy.
Lifestyle Factors That Support Treatment
Medication does the heavy lifting, but a few practical habits help it work as well as possible. Selenium and iodine are both essential for thyroid function. Most people in the U.S. get enough iodine from iodized salt and dairy, and selenium from foods like Brazil nuts, fish, and eggs. Unless your provider identifies a specific deficiency, supplements beyond a normal diet aren’t necessary and can sometimes cause harm.
Maintaining a consistent weight helps keep your dose accurate, since levothyroxine is weight-dependent. Large weight changes, in either direction, may require a dose adjustment. Exercise can help with some symptoms like fatigue and mood changes, though it won’t replace medication. If you’re planning a pregnancy, tell your provider early, since thyroid hormone needs increase significantly during pregnancy and dose adjustments should happen quickly.