Being tired has very similar effects on the body as drinking too much.
Being tired is usually linked to sleep deprivation. Sleep deprivation weakens crucial communication between the neurons in the brain, this can lead to lapses in memory and problems concentrating. This is in some ways comparable to being drunk.
This conclusion is very important considering the number of road accidents caused by tiredness. Being tired is more or less the same as being drunk at the wheel, as memory and decision making is impaired. There are some calls for similar traffic rules and regulations for the tired, as there are for driving under influence.