Final answer:
True, both barbiturates and benzodiazepines act on GABAA receptors to increase their activity, resulting in an inhibitory and depressant effect on the central nervous system.
Step-by-step explanation:
Barbiturates and benzodiazepines are both classes of drugs that directly act on the GABAA receptor and result in its activation, making the statement true. These substances are known to increase the activity of GABA receptors in the brain, which has an inhibitory effect on neuronal activity. Barbiturates increase the duration of the chloride channel opening, while benzodiazepines increase the frequency of the channel opening, both leading to an increased inhibitory effect and therefore have a depressant effect on the central nervous system. This synergistic effect can be extremely dangerous when these drugs are combined, especially in cases of overdose with other CNS depressants.