When I first met Tina, a woman in her late 20s, she had been seeing mental health professionals for virtually her entire life. “One day I’m energetic and creative,” she told me during one of our therapy sessions, “the next I am aimless, or I cry and feel worthless.” Tina had been diagnosed with depression, borderline personality disorder and even schizophrenia. Doctors prescribed antidepressants and later antipsychotics—but the meds only seemed to make her worse. At first I, too, saw her difficulties through the lens of a psychologist, thinking she had bipolar disorder. But later I noticed that her mood swings were accompanied by symptoms such as a racing heart, nausea and joint pain. So I asked her doctors to do a thorough blood workup.