The thyroid is a small gland in the front of your neck. It is shaped like a butterfly. It creates hormones for the regulation of heart rate, metabolism, and body temperature. The thyroid also plays a role in brain development and function. While the thyroid itself doesn't directly affect driving, its hormones can indirectly impact it. For example, suppose someone with hypothyroidism (an underactive thyroid) doesn't take their medication as prescribed.  In that case, they may experience fatigue and other symptoms that can make it difficult to focus on the task of driving. Additionally, some medications used to treat thyroid conditions can cause drowsiness or impair cognitive function, making it unsafe to operate a vehicle.