Consumption of large amounts of alcohol lowers normal social inhibitions and encourages inebriated people to indulge in riskier behaviors than normal, one of which is sometimes sending "drunk texts" to others. The National Institutes of Health report that a blood-alcohol level of as little as 0.01 can be associated with this loss of inhibition.
Sending texts while drunk has the same root cause as most of the unwise things people do after they've had too much to drink. Alcohol acts first on the cerebral cortex, which is the part of the brain that controls much of how people relate to one another and how they think about the consequences of their actions. Alcohol thus begins lowering inhibitions from the first drink. As a person drinks more, according to the chart on the NIH's website, the alcohol affects more and more of the brain and induces other symptoms, such as emotional arousal and aggression. These symptoms can influence a person's decision to grab the phone and start sending wildly irresponsible text messages to friends and acquaintances. The mood swings that typically set in at a blood alcohol level of between 0.11 and 0.20 can also motivate repeat texts as the drunk texter oscillates from feelings of affection to anger and depression.