You don't need to be drunk to experience problems at your work because of alcohol. Many performance problems are associated with relatively low blood alcohol levels due to e.g. drinking alcohol at lunch or heavy drinking the previous night. Alcohol, if not consumed reasonably and in appropriate circumstances, can reduce your work performance, both in the short and long term.
In the short term, increased blood alcohol levels endanger performance and safety. Even if you have drunk a small amount of alcohol, you are more likely to make mistakes. It also increases the likelihood of an accident.
In the long run, the constant consumption of large amounts of alcohol can create many social, psychological, and medical problems, including addiction. Continuous alcohol consumption often leads to low performance at work and increased absences due to illness. Those who drink for a long period of time face a sudden deterioration of their physical and interpersonal abilities.