Alcoholism falls under the category of toxic diseases.
When a person is drunk, he/she develops a disturbance of co-ordination. This results in double vision, slurring of speech (dysarthria), unsteadiness of the arms and legs, and ataxia of gait. These develop during a bout of drinking, and clear up some hours afterwards (usually with a hang over).
If excessive alcohol is taken over a long period of time, however, the effects differ. The toxin acts directly on the brain and liver, and also causes sufficient damage to the stomach to prevent the absorption of vitamins.
The direct effects consist of gross tremulousness of the whole body, followed a few days later by wild confusion and agitation with terrifying visual and auditory hallucinations, and absolute wakefulness. This is delirium tremens (D.Ts.), and occurs in chronic alcoholics who have had a heavy bout of drinking and then stopped.
Treatment is by sedation, and not by giving more alcohol, though this practice dies hard.
After years of heavy drinking, the deficiency of Vitamins causes severe damage to the brain stem. This results in mental confusion, paralysis of eye movements, double vision, ataxia of arms and legs, and in addition a polyneuropathy (i.e. the condition called Wernicke's encephalopathy) and must be treated with massive doses of Vitamin B.