The standard medicine for hypothyroidism is levothyroxine, a synthetic version of the hormone your thyroid can no longer produce enough of on its own. It comes as a daily pill, capsule, or liquid, and most people take it for life. While levothyroxine is the first-line treatment for nearly everyone, a few other options exist for specific situations.
How Levothyroxine Works
Your thyroid gland normally produces a hormone called T4, which your body then converts into the active form, T3, inside your tissues. When your thyroid is underactive, it doesn’t make enough T4 to keep that process running. Levothyroxine is a lab-made copy of T4 that replaces what’s missing. Once it’s in your bloodstream, your body converts it to T3 the same way it would with the natural hormone.
This approach works for the vast majority of people because it lets your body regulate its own T3 levels, converting as much or as little as it needs in each organ. Levothyroxine is classified as a “narrow therapeutic index” drug, meaning even small changes in dose can make a noticeable difference in how you feel. That’s why manufacturers are held to strict standards for the accuracy and consistency of each tablet.
How Dosing Is Determined
Your dose is based primarily on your body weight. The typical starting dose for healthy adults is about 1.6 micrograms per kilogram of body weight per day. For someone who weighs 150 pounds (68 kg), that works out to roughly 109 micrograms daily, though your doctor will round to the nearest available tablet size. Older adults usually start at a lower dose and increase gradually.
After you begin treatment (or after any dose change), you’ll have a blood test about six to eight weeks later to check your TSH level. TSH is the signal your brain sends to your thyroid telling it to work harder. When your replacement dose is right, TSH drops back into the normal range. Current guidelines aim for a TSH between 0.4 and 4 mIU/L, though your target may be narrower depending on your age and circumstances.
Taking It the Right Way
Levothyroxine is famously finicky about absorption. The classic advice is to take it on an empty stomach, 30 to 60 minutes before eating or drinking anything other than water. Coffee in particular has long been flagged as something to avoid right after your dose. However, newer liquid formulations appear to sidestep this problem. A study from Vertice Pharma found that an oral levothyroxine solution was absorbed equally well whether coffee was consumed five minutes later or not at all. If you take the standard tablet form, sticking with the 30-to-60-minute buffer before coffee or food is still the safer bet.
Calcium supplements, iron supplements, and antacids are the biggest absorption culprits. Take any of these at least four hours before or after your thyroid pill. The same applies to many multivitamins, since they often contain calcium or iron. Spacing them out is more important than most people realize: if you take your levothyroxine alongside a calcium pill every morning, you could be absorbing significantly less medication than your doctor prescribed.
Brand Name vs. Generic
Both brand and generic levothyroxine meet FDA standards for quality, strength, and purity, and several studies show similar effectiveness between the two. The active ingredient is the same. Where they can differ is in the inactive ingredients (fillers, dyes, binders), which may slightly affect how the drug is absorbed in your gut.
For most people, this difference doesn’t matter. But if your pharmacy switches you to a different generic manufacturer, the tablet may look different and absorb a little differently. It’s worth rechecking your thyroid levels six to eight weeks after any switch. Your provider may prefer you stay on a single brand in situations where consistent absorption is especially important, such as pregnancy, thyroid cancer follow-up, celiac disease, or after gastric bypass surgery. If you’re allergic to a dye or filler in one version, you can switch to another formulation with different inactive ingredients.
Combination Therapy: Adding T3
A small number of people take levothyroxine faithfully, get their TSH into the normal range, and still feel tired, foggy, or generally unwell. For some of these patients, adding a small dose of synthetic T3 (liothyronine) to their levothyroxine may help. A joint consensus statement from the American, British, and European thyroid associations acknowledges this as a reasonable option in select cases.
The patients most likely to benefit are those whose bodies don’t efficiently convert T4 to T3 on their own. This can happen due to genetic variations in the enzyme responsible for that conversion. The consensus criteria suggest combination therapy is most worth exploring in people already on an adequate dose of levothyroxine (at least 1.2 micrograms per kilogram per day), who have low-normal T3 levels in their blood, and who continue to have symptoms despite a normal TSH. It’s not a first step. It’s a targeted option after standard treatment has been optimized and found wanting.
Desiccated Thyroid Extract
Before synthetic levothyroxine existed, the only treatment was desiccated (dried) thyroid extract made from pig thyroid glands. It’s still available today and contains both T4 and T3. Some patients prefer it, and some practitioners prescribe it as an alternative.
The key difference is the hormone ratio. Pig thyroid glands contain proportionally more T3 relative to T4 than the human thyroid produces. That higher T3 content can cause T3 levels to spike after each dose, which makes precise dosing trickier. Desiccated thyroid extract is not recommended as a first-line treatment by major endocrinology guidelines, but it remains an option some people use, particularly those who haven’t felt well on levothyroxine alone.
Risks of Taking Too Much
Because levothyroxine has such a narrow dosing window, overtreatment is a real concern. Taking more than your body needs pushes you into a state of excess thyroid hormone, which over time carries measurable health consequences.
Bone loss is one of the most well-documented risks. A study with a median follow-up of 6.3 years found that levothyroxine use was associated with greater loss of total body bone mass and bone density, even in people whose TSH levels stayed within the normal range. Excess thyroid hormone has also been linked to an increased risk of bone fractures and irregular heart rhythms. These findings are especially relevant for older adults, a group where some research suggests thyroid hormone may sometimes be prescribed without a clear indication.
The practical takeaway: more is not better. Dose adjustments should always be guided by blood work, and routine monitoring matters even after you’ve been on a stable dose for years.
Adjustments During Pregnancy
If you’re on levothyroxine and become pregnant, your dose will almost certainly need to go up. The American Thyroid Association recommends increasing your dose by 20 to 30 percent as soon as pregnancy is confirmed, then checking levels frequently throughout the pregnancy. This early bump helps avoid even a brief period of low thyroid hormone, which is important for fetal brain development in the first trimester. After delivery, most women return to their pre-pregnancy dose.