Diarrhea can be a symptom for individuals taking Synthroid (levothyroxine). While not everyone experiences this side effect, it is a recognized possibility.
Understanding the Connection
Synthroid, a synthetic thyroid hormone, works to replace the hormone naturally produced by the thyroid gland. Diarrhea, as a side effect of levothyroxine, is often linked to changes in thyroid hormone levels. When thyroid hormone levels become elevated—due to an initial dose, a dose adjustment that is too high, or individual sensitivity—it can lead to symptoms mimicking hyperthyroidism.
Elevated thyroid hormone increases gut motility. This means that digestive contents move more rapidly through the intestines, allowing less time for water absorption and resulting in loose stools. This accelerated transit time can also lead to malabsorption in some cases.
Issues with Synthroid absorption can also indirectly contribute to digestive upset. Certain foods (like soybean flour, walnuts, dietary fiber), other medications (like iron, calcium supplements, antacids), or underlying gastrointestinal conditions can interfere with levothyroxine absorption. This can lead to fluctuating hormone levels, causing symptoms when the medication’s effect is higher or lower than intended.
In rare instances, individuals might experience a reaction to the inactive ingredients, known as excipients, found in Synthroid tablets. These components can sometimes cause gastrointestinal irritation. Diarrhea can stem from various unrelated health conditions, but if it coincides with starting or adjusting Synthroid, it is reasonable to consider the medication as a potential factor.
Managing Diarrhea Symptoms
If you experience diarrhea while taking Synthroid, several measures can help manage symptoms. Staying well-hydrated is important to prevent dehydration. Drink plenty of water, clear broths, and electrolyte solutions to help replenish lost fluids and minerals.
Adjust your diet to include bland, easy-to-digest foods such as bananas, rice, applesauce, and toast. It is advisable to temporarily avoid foods that can worsen symptoms, including fatty, spicy, and high-fiber foods, as well as dairy products and caffeine.
Keep a detailed record of your symptoms, noting the frequency and consistency of bowel movements and any other accompanying symptoms. This information can help your doctor assess the situation and determine if a Synthroid dosage adjustment or other interventions are needed. Do not take over-the-counter anti-diarrheal medications without consulting your doctor, especially if the diarrhea is linked to your medication.
When to Seek Medical Advice
Contact your doctor if you experience severe or persistent diarrhea while on Synthroid. Diarrhea that does not improve, worsens, or significantly interferes with daily activities requires medical attention. Watch for signs of dehydration, such as extreme thirst, reduced urination, dizziness, or unusual fatigue, as these indicate a need for prompt evaluation.
Other concerning symptoms requiring immediate medical consultation include fever, intense abdominal pain, or the presence of blood or black color in your stools. Unexplained weight loss should also be reported to your doctor. If you develop new or worsening symptoms of hyperthyroidism—such as a rapid heart rate, tremors, increased anxiety, excessive sweating, or heat intolerance—these could signal that your Synthroid dose is too high.
Always consult your prescribing doctor before changing your medication dosage or stopping Synthroid. Your doctor can assess your thyroid hormone levels and determine the appropriate course of action, including adjusting your dosage or exploring other potential causes for your symptoms.