Lifestyle

Feeling Jittery or Always Cold on Thyroid Medicine Can Mean Your Dose Needs a Check. Signs to Tell Your Doctor

By Erica Coleman · November 4, 2026

Nearly 5 out of 100 Americans ages 12 and older have hypothyroidism, an underactive thyroid, and it is more common in people older than 60, according to the National Institute of Diabetes and Digestive and Kidney Diseases. The usual treatment is a daily thyroid hormone pill called levothyroxine.

Getting the dose right matters, and it can take time. Doctors usually start with a low dose and raise it gradually, MedlinePlus says. The dose may also change over the years. That is why it helps to know what the body tends to say when the amount is off.

Start with the signs that the dose may be too high. The American Thyroid Association says too much medicine can make you feel nervous, have a fast heartbeat, feel hot or lose weight. MedlinePlus lists symptoms to tell your doctor about while taking levothyroxine, including:

Heart changes. Chest pain or a rapid or irregular heartbeat or pulse.

Shakiness and nerves. Uncontrollable shaking of part of the body, nervousness, anxiety or irritability.

Poor sleep. Trouble falling asleep or staying asleep.

Other changes. Shortness of breath, excessive sweating or sensitivity to heat.

Too much thyroid hormone medicine can cause serious problems, such as atrial fibrillation, an irregular heart rhythm, NIDDK warns.

The opposite problem looks different. With too little medicine, the ATA says, you may still feel tired, cold or constipated. MedlinePlus notes that without enough thyroid hormone, people can have a lack of energy, weight gain, dry skin, joint and muscle pain and greater sensitivity to cold. If symptoms like these come back or get worse, the ATA says to call your doctor.

Everyday habits matter too. Some common products can affect how well the pill works, which can make a steady dose act like the wrong one.

Calcium and iron. MedlinePlus says to take calcium carbonate or ferrous sulfate, an iron supplement, at least 4 hours before or 4 hours after levothyroxine.

Heartburn medicines. MedlinePlus lists proton pump inhibitors and antacids among the nonprescription products that may interact with it, along with aspirin and some other pain relievers.

Certain foods. Soybeans, walnuts and dietary fiber may affect how it works, according to MedlinePlus, which suggests talking with your doctor before eating them. It also suggests asking about grapefruit.

Timing. It is usually taken once a day on an empty stomach, 30 minutes to 1 hour before breakfast, MedlinePlus says.

The ATA also advises calling your doctor if you gain or lose 10 pounds or more, or if you start or stop a medicine that affects thyroid pills, such as antacids, calcium or iron supplements, biotin or estrogen.

A blood test is how the dose gets checked. Your doctor will check your blood about 6 to 8 weeks after you start or change your dose, the ATA says. Once you reach a dose that works, NIDDK says, the test is usually repeated in 6 months and then once a year.

Never stop or change your dose on your own. “Never stop taking your medicine without talking with your doctor first,” NIDDK says. If something feels off, write down what you notice and when, list every supplement and over-the-counter medicine you take, and bring it to your next appointment or call sooner.

This article is for general information and is not medical advice. Do not stop or change any medicine without talking with the doctor who prescribed it. This article was produced with the assistance of AI and fact-checked against the sources cited by LightWave Reports.