Synthroid Side Effects

Synthroid is a synthetic hormone that is used to treat hypothyroidism by replacing the hormones that are not being produced due to a malfunctioning thyroid gland. Typically, this medication will be prescribed for life, so your prescription will alter as your condition changes and as you age. Regular monitoring of your thyroid and hormone levels will be necessary in order to determine the proper dosage of your Synthroid prescription.


Dosage for Synthroid will vary greatly depending on the age, weight and medical conditions found in the patient. Periodic adjustments to the dosage will be determined with laboratory testing. Typically, patients are asked to take their prescription half an hour before they eat breakfast. Any additional doses will be taken at least 4 hours apart to ensure proper absorption of the medication. It may take up to 4-6 weeks for the proper effects to start taking shape. If any aspect of your medical condition changes, inform your doctor so they can determine whether or not a change in your Synthroid prescription is necessary. This includes any new medications you might be taking or changes in physical conditions including cardiovascular disease or hormonal peaks.

Common Side Effects of Synthroid

Instances of Synthroid side effects are not particularly common, typically occurring in less than 1 percent of users. The most common of these include change in appetite, diarrhea, headache, leg cramps, and shortness of breath, vomiting or weight loss. Hormonal changes have also brought on excessive sweating, chest pain, irregular heartbeat, fever, hair loss, tremors, irritability, heat tolerance or changes in menstrual symptoms. In most cases these symptoms were temporary and not severe enough to prompt the patient to stop taking Synthroid. You should not stop taking your medication suddenly if you begin to experience Synthroid side effects. Instead, consult your doctor about an appropriate way to address the particular condition you have developed.

Some people may experience an allergic reaction to the ingredients in Synthroid. If you begin to develop irregular heartbeat, swelling, hives, shortness of breath or excessive headache, that are severe in nature contact emergency medical services for support. If you have been taking Synthroid regularly prior to these symptoms developing you could be reacting to an increase in your dosage. Contact your doctor regarding whether or not you should continue your medication at the current rate. It is more than likely that your doctor will reduce your dosage to help combat the symptoms you have begun to exhibit.

Uncommon and Rare Side Effects of Synthroid

In very rare cases, Synthroid users saw instances of heart attacks, seizures, angina, mood changes, and head pain, changes in pulse, stomach cramps, muscle weakness and low energy. These symptoms were significantly increased in those who already suffered from a heart condition. Give your doctor a full report of your medical history, making special note of any other hormonal or cardiovascular conditions you have already been treated for. Any medications that are being used to treat these conditions should be reported as well. This knowledge can help your doctor determine your risk for developing side effects while on Synthroid. If at any time you develop cardiovascular distress, seek emergency attention as soon as possible. Most other side effects associated with Synthroid tend to be mild, but contact your doctor to inform them about any of these conditions to determine if it is safe to continue your current dosage.

Side Effects in Children, Pregnant Women and Seniors

Infants may receive up to 15 mg per day of Synthroid, unless they have been flagged at-risk for cardiac failure. Children who have not yet reached puberty will start with the minimum dose and increase their dosage as they grow or reach a new hormonal level.

There is no threat for women taking Synthroid while pregnant. However, your dose will need to be adjusted to cope with the altered hormone levels that occur at this time. Inform your doctor if you are attempting to become pregnant or if you have just discovered you are pregnant so they can adjust your dosage accordingly.

Patients over the age of 50 will need to adjust their dosage to meet their declining hormone levels. This is especially relevant for those who suffer from cardiac disease or those in the midst of menopause. If you have recently been diagnosed with hyperthyroidism at an advanced age, it is likely that you will be started at the minimum dose and have your dosage increased gently as necessary. If you are using Synthroid to address secondary or tertiary hypothyroidism, you may only use the drug in combination with other substances until your hormone levels return to their normal state.

Interactions with Other Medications and Substances

Any medications that contain calcium carbonate or ferrous sulfate iron should be avoided while on Synthroid. Foods that contain cotton seed meal, walnuts, and high amounts of fiber or infant soy formula are also not recommended. These items can lower the absorption rate of the medication. Any medications that contain sodium polystyrene sulfonate, aluminum (notably antacids), or cholesterol-lowering medication should not be taken within 4 hours of taking Synthroid as they can make the drug less effective. Do not change brands for any of your regular medications until you have spoken to your doctor about the ingredients. Inform your doctor regarding any medications you are currently taking so they can recommend a proper dosage schedule for you.