Which of the following is a notable side effect of barbiturates?

Tolerance is a notable side effect of barbiturates because prolonged use of these medications leads to a decreasing effect over time. The body adapts to the presence of the drug, resulting in the need for higher doses to achieve the same therapeutic effect. This phenomenon is particularly important for barbiturates, as they have a narrow therapeutic index and the development of tolerance can lead to an increased risk of overdose and related complications.

In the context of the other options, while dry mouth may occur as a side effect due to anticholinergic properties in some medications, it is not as significant or characteristic of barbiturate use. Hyperactivity is generally not associated with barbiturates, as they are primarily depressants of the central nervous system. Priapism, although a serious condition, is more commonly linked to medications such as PDE5 inhibitors or certain antidepressants, rather than barbiturates. Therefore, tolerance stands out as a prominent and concerning side effect in the context of barbiturate usage.