Which of the following may occur with excessive use of barbiturates?

Excessive use of barbiturates is primarily associated with respiratory depression, which is a serious and potentially life-threatening condition. Barbiturates are central nervous system depressants that can significantly slow down brain activity, leading to a reduction in the respiratory drive. This inhibition can lead to inadequate breathing, decreased oxygen levels in the blood, and ultimately respiratory failure if not managed appropriately.

While severe headaches, nausea and vomiting, and dry mouth can occur with various medications or other illnesses, they are not the most critical or life-threatening side effects associated with barbiturate overdose. Respiratory depression directly impacts the body's ability to sustain essential functions, making it the most relevant concern in the context of excessive barbiturate use.