The common side effects of low T4 hormone levels include hand tremors, increased heart rate, hair loss, dry skin and dryness, irritation, puffiness or bulging of the eyes, according to Healthline. Other symptoms include change in weight, insomnia, anxiety, fatigue, light sensitivity and irregular menstrual.
The thyroid produces hormones that are released into the blood and transported to the rest of the body. These hormones help the body utilize the energy, keep warm, and maintain the brain, heart muscles and other organs. A thyroid-stimulating hormone test measures T4 levels and helps doctors diagnose thyroid disorders such as hyperthyroidism, hypothyroidism, hypopituitarism and thyrotoxic periodic paralysis, according to the American Thyroid Association.