Drowsiness after taking cold medicine usually disappears after 4-6h when the drug is metabolized. The reason why you get sleepy after taking cold medicines is that current cold medicines are compound preparations, and some cold medicines contain antihistamine ingredients, such as chlorpheniramine maleate, also known as paracetamol, which is a histamine receptor blocker. This ingredient has a strong fat solubility, in the role of at the same time can also be through the blood-brain barrier directly on the nerve center, the nerve center has an inhibitory effect. So some people will be very sleepy after taking cold medicine containing chlorpheniramine maleate, which is a normal reaction of the drug, and the drowsiness will disappear after the drug is over. After taking cold medicines containing this ingredient, it is not recommended to do work at heights and fine work, or to drive a car, sail a boat, or fly an airplane to avoid danger. If the nature of the work requires the above operations, it is recommended to take cold medicines that do not contain antihistamines.