Thyroid medications. Levothyroxine (Synthroid), which treats hypothyroidism — an underactive thyroid — should be taken on an empty stomach at least 30 minutes before food, or alternatively, three to four hours after the last meal of the day, Hess says. Additionally, levothyroxine should not be taken within four hours of food or drink that contains calcium or iron. “Therefore, if you enjoy adding milk to your morning cereal or drinking a glass in the morning, discuss timing of your levothyroxine or switching your dose to bedtime with your provider,” Hess says. If your routine includes consuming these products earlier than four hours, it’s important to monitor thyroid levels; if the tests are normal, it’s probably okay to be flexible about timing — but, again, it’s key to discuss this with the doctor, she says.