The causes of drowsiness in the elderly may be sleep deprivation at night, drug factors, systemic diseases or brain diseases. 1. Lack of sleep at night: Most of the elderly people may suffer from disruption of sleep biorhythms due to brain atrophy, which leads to sleep deprivation at night and drowsiness during the day. 2. Drug factors: some patients may take sleeping drugs because of insomnia, which may cause drug unresponsiveness or prolonged drug effect due to decreased liver and kidney functions, thus showing drowsiness. 3. Systemic diseases: such as diabetes mellitus, hypothyroidism, leading to metabolic abnormalities in the elderly; chronic liver disease, renal disease, etc., leading to systemic internal environmental disorders; heart disease leading to insufficient blood supply to the whole body, etc. can lead to drowsiness symptoms. 4. Brain diseases: such as cerebral hemorrhage, cerebral infarction, brain tumor, which can affect the blood supply to the brain or influence the consciousness, thus resulting in drowsiness. If the elderly have drowsiness, they should seek medical treatment in time.