We asked a doc to break it down.
If you're gaining weight for no reason, pooping less frequently, feeling like you always need moisturizer, are tired all the time even though you get enough sleep, or you notice your hair is thinning or your nails keep breaking, you may be suffering from an underactive thyroid, or hypothyroidism, where you're not producing enough thyroid hormone.
Symptoms of an overactive thyroid (hyperthyroidism), on the other hand, include unexplained weight loss, frequent sweating, a rapid heartbeat, softer poop, and (again) fatigue.
Even if you aren't experiencing any of these issues, there are other factors that suggest a thyroid blood test may be in order. Having another autoimmune disease (like type 1 diabetes), pernicious anemia, a first-degree relative with thyroid problems, certain psychiatric conditions, or taking the mood meds amiodarone or lithium have all been linked with thyroid dysfunction. (It's common to test people who experience depression with no family history or no causal life circumstances, and people with anxiety who show some of the physical symptoms too.) Your primary-care doc can schedule the test for you.