Hypothyroidism is treated with a daily pill that replaces the thyroid hormone your body isn’t making enough of. The standard medication is levothyroxine, a synthetic version of the hormone thyroxine (T4), and most people take it for the rest of their lives. Treatment is straightforward, but getting the dose right, taking it correctly, and monitoring your levels over time all matter for feeling your best.
How Levothyroxine Works
Your thyroid normally produces two hormones: about 80% thyroxine (T4) and 20% triiodothyronine (T3). Your body then converts about half of that T4 into T3, the more active form that directly influences your metabolism. Levothyroxine is a synthetic copy of T4. Once you take it, your body converts it into T3 just as it would with naturally produced hormone, restoring normal function.
These thyroid hormones enter your cells and influence how your body uses energy, makes proteins, and processes sugar. That’s why low thyroid levels affect so many different systems at once, causing fatigue, weight gain, brain fog, cold sensitivity, and dozens of other symptoms. Replacing the missing hormone addresses all of them at the source.
Starting Dose and Adjustments
The typical full replacement dose is about 1.6 micrograms per kilogram of body weight per day. For a 150-pound adult, that works out to roughly 100 to 125 micrograms daily. But not everyone starts at the full dose. Older adults and people with heart conditions typically begin at a much lower dose, around 12.5 to 25 micrograms per day, and increase gradually every 6 to 8 weeks until their levels normalize. This slow approach protects the heart from a sudden surge in metabolism.
Your provider checks your TSH (thyroid-stimulating hormone) level about 6 to 8 weeks after you start, since that’s how long it takes for levels to stabilize on a given dose. If TSH is still high, the dose goes up. If it drops too low, you’re getting too much. This adjustment process can take a few rounds, so expect several months before your dose is dialed in. After that, most people get their TSH checked once or twice a year.
When You’ll Start Feeling Better
Most people notice improvement within one to two weeks of starting treatment. Energy often picks up first, followed by gradual improvements in mood, concentration, and other symptoms over the following weeks. Full symptom resolution can take longer, especially for issues like dry skin, hair thinning, or elevated cholesterol, which may need several months to fully reverse. The key is patience during the dose-adjustment phase. If you still feel off after your levels have been in the normal range for a couple of months, that’s worth raising with your provider.
How to Take It Correctly
Levothyroxine is surprisingly finicky about absorption. You should take it on an empty stomach, ideally first thing in the morning, and wait at least 30 to 60 minutes before eating or drinking anything other than water. Coffee alone can reduce absorption by about 32%, and milk reduces it by around 10%. Even small, consistent changes in how you take it can shift your effective dose enough to throw off your levels.
Several common supplements and medications interfere significantly with absorption:
- Calcium supplements reduce absorption by about 31%, regardless of the type (carbonate, citrate, or acetate). Space them at least 4 hours apart from your thyroid pill.
- Iron supplements form a chemical complex with the medication that your body can’t absorb well. Same 4-hour rule applies.
- Antacids containing aluminum or magnesium can raise TSH dramatically. One study found TSH nearly tripled in patients taking aluminum hydroxide alongside levothyroxine.
- Proton pump inhibitors (commonly used for acid reflux) reduce stomach acidity, which the pill needs to dissolve properly. Most studies confirm this interaction, though the effect varies by person.
- Cholesterol-lowering resins like cholestyramine bind so aggressively to the hormone that absorption can drop to nearly zero if taken at the same time.
The simplest strategy: take levothyroxine first thing in the morning with plain water and push everything else to later. If you take calcium or iron, aim for lunchtime or later.
Combination Therapy With T3
About 10 to 15% of people on levothyroxine alone continue to feel unwell despite having normal lab results. For these patients, adding a small amount of synthetic T3 (liothyronine) is sometimes considered. European Thyroid Association guidelines from 2013 suggest this as an option after other causes of persistent symptoms, like depression, sleep disorders, or iron deficiency, have been ruled out.
People with particularly low T3 blood levels while on standard therapy, and those who’ve had their thyroid surgically removed (and therefore produce no hormone on their own), tend to be the most likely candidates. Combination therapy is not recommended during pregnancy or for people with heart rhythm problems or cardiovascular disease, since T3 acts faster and more potently than T4 and can increase heart rate.
Desiccated Thyroid Extract
Desiccated thyroid extract, sold under brand names like Armour Thyroid, is made from pig thyroid glands and contains both T4 and T3. It predates synthetic levothyroxine by decades. Most medical guidelines still recommend synthetic T4 as the first-line treatment, citing concerns about the fixed T4-to-T3 ratio in animal-derived products not matching what the human thyroid produces.
That said, research has found that quality of life improves similarly with both options, and desiccated thyroid is associated with modest weight loss of about 4 pounds compared to levothyroxine alone. In one well-designed study, nearly half of patients preferred desiccated thyroid over synthetic T4. The main measurable trade-off was a small increase in heart rate. For people who feel well on levothyroxine, there’s no reason to switch. For those who don’t, it’s a reasonable conversation to have.
Subclinical Hypothyroidism
Subclinical hypothyroidism means your TSH is elevated but your actual thyroid hormone levels are still in the normal range. You may have mild symptoms or none at all. Treatment decisions here depend largely on how high your TSH is.
When TSH is above 10 mIU/L, treatment with levothyroxine is generally recommended because the risk of progressing to full hypothyroidism is significant, and these patients face higher rates of cholesterol problems, cardiovascular events, and mood disturbances. About 90% of people with subclinical hypothyroidism, however, have TSH levels between 4 and 10 mIU/L. For this group, the decision is less clear-cut. Treatment is more likely to be started if you have symptoms, thyroid antibodies (suggesting autoimmune thyroid disease), elevated cholesterol, a visible goiter, or fertility concerns.
Treatment During Pregnancy
Pregnancy increases the body’s demand for thyroid hormone substantially. If you’re already on levothyroxine, the standard recommendation is to increase your dose by 30 to 50% as soon as pregnancy is confirmed, usually by adding about 50 micrograms per day. Thyroid levels should then be checked every 4 weeks during pregnancy.
The TSH targets are also tighter than usual: no higher than 2.5 mIU/L in the first trimester and no higher than 3.0 mIU/L in the second and third trimesters. Untreated or undertreated hypothyroidism during pregnancy raises the risk of complications including preeclampsia, preterm birth, and developmental effects on the baby, so close monitoring matters more than at any other time.
Long-Term Monitoring
For most people with hypothyroidism, the target is a TSH level within the normal reference range, typically between about 0.5 and 4.5 mIU/L, though the specific range varies slightly between labs. Once your dose is stable, annual or twice-yearly blood work is usually enough. Your dose may need adjusting over time due to weight changes, aging, pregnancy, or starting new medications that affect absorption.
If your TSH is in range but you still have symptoms, it’s worth looking at other potential contributors before assuming the thyroid medication needs changing. Iron deficiency, vitamin D deficiency, sleep apnea, and depression can all mimic or worsen hypothyroid symptoms. Addressing those alongside thyroid treatment often makes a bigger difference than fine-tuning the levothyroxine dose alone.