Underactive Thyroid: Causes, Symptoms, and What You Can Do

When your underactive thyroid, a condition where the thyroid gland doesn't produce enough hormones to keep your metabolism running properly. Also known as hypothyroidism, it affects millions of people—often without them realizing it’s the root of their fatigue, weight gain, or brain fog. Your thyroid is a small butterfly-shaped gland in your neck, but it controls how your body uses energy. When it slows down, everything from your heart rate to your mood gets affected.

Most cases of underactive thyroid are caused by Hashimoto’s disease, an autoimmune condition where your immune system attacks your thyroid gland. Other common causes include radiation treatment, thyroid surgery, or certain medications like lithium. Even iodine imbalance—too little or too much—can trigger it. Doctors usually check TSH levels, a hormone your pituitary gland releases to signal your thyroid to work harder. High TSH means your thyroid isn’t responding, even though your body is begging it to.

Common symptoms include constant tiredness, dry skin, hair loss, constipation, and feeling unusually cold. Women are far more likely to develop it, especially after pregnancy or around menopause. Many people dismiss these signs as stress or aging, but untreated underactive thyroid can lead to higher cholesterol, heart problems, or even depression. The good news? It’s one of the easiest hormone issues to fix—with daily medication like levothyroxine, which replaces the missing thyroid hormone. Most people feel better within weeks, but finding the right dose takes time and patience.

What you won’t find in drug ads is how often people struggle with inconsistent symptoms even after starting treatment. Some need to switch brands, others need to check for nutrient gaps like iron or vitamin D, which can block thyroid hormone absorption. And yes, your diet matters—not because you need to avoid soy or cruciferous veggies, but because skipping meals or extreme low-carb diets can slow your metabolism even more.

Below, you’ll find real-world guides on how thyroid meds interact with other drugs, what lab tests actually mean, how to spot when your dose is off, and why some people still feel awful even when their numbers look "normal." These aren’t theory pieces—they’re from people who’ve been there, tested the options, and figured out what works.