It’s a common story: your bone-numbing fatigue, inability to sleep, brain fog, aches and pains, headaches, depressed mood, hair loss, low sex drive, and the weight gain you can’t control—no matter how many calories you cut—finally drive you to the doctor. You’re diagnosed with hypothyroidism and given a prescription for levothyroxine, which you take faithfully. But the weeks go by, and you don’t feel any better.