Levothyroxine intolerance: how to tell and what to do

Does your levothyroxine make you jittery, tired, or just not better? That’s frustrating—and more common than people think. "Intolerance" can mean different things: an allergic reaction to fillers, true side effects from too much hormone, or poor absorption so the drug doesn’t work. This short guide helps you spot the difference and take smart next steps.

Why levothyroxine might feel wrong

There are a few clear reasons your body objects to the pill:

• Wrong dose: Too much causes palpitations, anxiety, sweating, and weight loss. Too little leaves fatigue and slow thinking—both feel like "it’s not working."
• Absorption problems: Calcium, iron, antacids, soy, and some gut issues (like celiac or H. pylori) cut how much drug gets into your blood.
• Reaction to excipients: Some people react to fillers or dyes in tablet brands. That looks like rashes, stomach upset, or general malaise after taking pills.
• Interaction with other meds: Cholestyramine, proton-pump inhibitors, estrogen changes, and some supplements change levothyroxine levels.
• Miscalculated diagnosis: Symptoms can come from anxiety, adrenal problems, or other illnesses, not the thyroid pill itself.

Practical steps if you think you’re intolerant

Don’t stop your medicine suddenly. Here’s a safe, useful plan you can follow with your doctor.

• Check bloods: Get TSH and free T4 (and sometimes free T3). If TSH is too low, dose is likely high. If TSH stays high despite pills, absorption may be the issue.
• Review timing: Take levothyroxine on an empty stomach 30–60 minutes before breakfast or at bedtime 3–4 hours after eating. Avoid calcium, iron, antacids within four hours.
• Scan your meds and supplements: Tell your doctor about everything you take—some common over-the-counter products interfere.
• Try a different formulation: If you suspect fillers, ask about Tirosint (gel caps with fewer ingredients), liquid levothyroxine, or a compounded form. Many people who react to tablets do fine on these.
• Consider alternatives carefully: Liothyronine (T3) or a T4/T3 combo and desiccated thyroid exist, but they have pros and cons. Discuss risks, monitoring, and goals with your clinician.
• Check for GI causes: If absorption is suspected, test for celiac disease, H. pylori, or low stomach acid.

If symptoms are severe—hives, swelling, trouble breathing—seek emergency care. For less urgent signs, schedule a focused visit with your provider, bring a list of meds and symptoms, and ask for repeat labs after any change. Fixing levothyroxine problems is usually straightforward once you find the cause, so keep pushing until you get an answer that fits you.