Fibromyalgia may lead to weight gain caused by hormonal imbalances sending out excess hunger signals, in turn causing people to eat more. Certain medications used to treat fibromyalgia can cause weight gain as well. Fibromyalgia’s associated symptoms, such as extreme pain and achiness, can limit a person’s mobility so they are unable to exercise or cook. Sleep deprivation, a common symptom of fibromyalgia, commonly slows down the metabolism and increases a person’s appetite (to supplement for the lack of energy), resulting in weight gain.