Which of the following symptoms is characteristic of both Diazepam and MAOIs?

The characteristic symptom that both Diazepam and MAOIs can produce is mydriasis, which is the dilation of the pupils.

Diazepam, a benzodiazepine, primarily acts by enhancing the effects of the neurotransmitter gamma-aminobutyric acid (GABA) at GABA-A receptors, leading to various central nervous system effects, including muscle relaxation and sedation. Mydriasis can occur as a result of its central nervous system effects, particularly in cases of overdose or excessive sedation.

Monoamine oxidase inhibitors (MAOIs) are primarily used as antidepressants and work by inhibiting the enzyme monoamine oxidase, which breaks down neurotransmitters like norepinephrine and serotonin. This leads to increased levels of these neurotransmitters, which can have a stimulating effect on the sympathetic nervous system, sometimes resulting in mydriasis as a sympathetic response.

Understanding that mydriasis occurs in both cases highlights the overlap in some pharmacological effects of these diverse medication classes, despite their different mechanisms of action. The other options, while they relate to various pharmacological effects, are not common effects associated with both Diazepam and MAOIs, making mydriasis the most appropriate choice.