Final answer:
The least sedating tricyclic antidepressant among the choices provided is Desipramine. It tends to have fewer sedative side effects compared to other tricyclics like amitriptyline or trimipramine.
Step-by-step explanation:
The least sedating of the tricyclic antidepressants listed is A. Desipramine. Tricyclic antidepressants, such as amitriptyline, imipramine, and others, are known for their sedative effects, which can include sleepiness, lightheadedness, and a decrease in blood pressure. However, desipramine tends to be less sedating compared to other tricyclic antidepressants like amitriptyline, trimipramine, doxepin, and imipramine. The sedative effects of tricyclic antidepressants are not desirable for some patients, which is why those with sedative side effects are not prescribed on an "as-needed" basis and why it's important to select the least sedating option when possible.