Both levothyroxine and Synthroid can cause similar side effects, primarily due to dosage issues or individual sensitivities. Remember, these medications are essentially the same active ingredient, but minor differences in inactive ingredients might trigger reactions in some people.
Common Side Effects:
Weight changes: Unexpected weight gain or loss is possible with both. Dosage adjustments often resolve this. Gastrointestinal issues: Nausea, diarrhea, or constipation are reported with both medications. Consider taking the medication with food if these issues arise. Changes in heart rate: Both can slightly increase or decrease heart rate. Report any significant changes to your doctor immediately. Muscle weakness or cramps: This can occur with both drugs. Your doctor may suggest adjustments to your dosage or further testing. Sleep disturbances: Insomnia or excessive sleepiness can be reported with either medicine. Taking the medication at the same time daily and avoiding taking it too close to bedtime may help. Hair changes: Both might cause hair thinning or increased hair growth. This usually improves once the correct thyroid hormone level is established. Changes in mood: Anxiety, irritability, or depression are possible. Regular blood tests ensure your thyroid hormones are correctly balanced.
Less Common, but Serious Side Effects:
Rare but serious side effects such as irregular heartbeat (arrhythmia) or allergic reactions require immediate medical attention. These are infrequent, but prompt action is crucial if they occur. While both medications share a potential for such reactions, their frequency remains exceptionally low. Always inform your doctor about any new or worsening symptoms.
