Many people claim to have tips and tricks that allow them to drink without becoming too drunk to drive. The fact is that alcohol impairment begins earlier than most people think. Physical effects can be present even before a person reaches the legal limit, which is .08 blood alcohol concentration (BAC). The Centers for Disease Control and Prevention breaks down the effects of alcohol, some of which may be surprising. 

0.6 ounces of pure alcohol is considered equal to a standard drink size. For instance, 12-ounces of beer with 5% alcohol content would be considered a single drink, as would 1.5-ounces of 80-proof distilled spirits, such as whiskey. Going by these standards, about two drinks would bring a person to .02 BAC. At this point, a person experiences a change in mood, as well as minimal impairment of judgment. In terms of driving, this can cause visual disturbances, as well as problems performing two activities at the same time. 

After three drinks, the effects become even more pronounced. A person’s BAC will rise to .05, which means alertness is diminished, while judgment becomes impaired even further. A person may also experience problems with visual focusing or experience difficulty tracking a moving object. Four drinks increases BAC to .08, which is the legal limit for driving. Problems concentrating, loss of short-term memory, and issues with perception usually occur at this level. 

Five or more drinks cause even more serious effects. BAC of .15 is linked to significant impairment. Loss of balance typically occurs, as does loss of muscle control. A person may also become physically ill, especially those lacking a tolerance to alcohol. Driving a vehicle is extremely dangerous, as a person will likely be unable to sufficiently control a vehicle or process information in a reasonable manner.