Headaches occur after drinking alcohol mainly because: 1. During the metabolism of alcohol in the body, a large amount of acetaldehyde is produced through ethanol dehydrogenase in the liver, and acetaldehyde can lead to dilatation of blood vessels in the periphery. It can also lead to intracranial vasodilation, so headaches can occur. 2, alcohol contains complex acid can stimulate the body to secrete a large number of catecholamines, catecholamines include adrenal hormone, norepinephrine and dopamine. When the body increases catecholamines can lead to sympathetic excitement, when acetaldehyde is metabolized in the body, blood vessels can be contracted with the increase in catecholamines, which can also lead to headache symptoms. 3, the alcohol content increases after drinking a lot of alcohol, because alcohol itself will stimulate the nerves in the brain, resulting in insufficient blood supply to the brain and increased nerve sensitivity, which can lead to headache symptoms after drinking alcohol.