The right answer is potential drug dependence.
The use of barbiturates was widespread in the first half of the twentieth century.
In the case of chronic abuse a tolerance to barbiturates, a physical and psychological dependence develops very quickly. Tolerance in particular results in a narrowing of the area between the dose needed to achieve the desired effect and the lethal dose. At some point, the required dose becomes greater than the lethal dose, resulting in coma and death without urgent medical management.
