As soon as our body starts to feel off, we immediately consider two explanations: Mercury is in retrograde, or there must be something wrong with our thyroid, according to Google. (Hint: Only one has solid science to back it up.) But can we really blame unwanted symptoms—from exhaustion to weight gain—on the thyroid, or is our scapegoating unwarranted?
The Need-to-Know 
Turns out, you’re not wrong for thinking of it first. Almost every system in our body depends in some part on hormones produced by the thyroid, says Jordan Geller, M.D., attending physician and past clinical chief in the Division of Endocrinology at Cedars-Sinai in Los Angeles.
The gland, found in the front part of the neck and about the size and shape of a small butterfly, plays a role in metabolism, growth, and just about everything in your body, from the brains to the bowels to the heart, skin, and digestive system.
How does it work? The thyroid produces a hormone, thyroxine (or T4) that goes out to all our organs. Once it arrives at its destination organ, it’s converted into another hormone, triiodothyronine (or T3). There, it sets the pace for your cells, helping them do what they’re supposed to do. Basically, those hormones tell your heart to keep beating, your liver to…