Reasons for headache the day after drinking alcohol: 1. The main reason is that alcohol contains heteroethanol oil, which is a toxic substance to the body and can stimulate the body to cause headache symptoms. 2. 4. Ethanol is metabolized in the liver into acetaldehyde, which produces acidic metabolites that stimulate the body to release pain-causing substances and lead to headaches. Therefore, after drinking alcohol, it is necessary to drink more honey water and sugar water to promote the transformation of alcohol in the body and promote the metabolism of alcohol. It is important to get enough sleep and rest after drinking alcohol to avoid the symptoms of headache caused by alcohol the next day after drinking.