**Core Concept**
The question tests the student's understanding of the pharmacological effects of **tricyclic antidepressants (TCAs)**, specifically **imipramine**. Imipramine is a TCA used to treat **major depressive disorder** and other conditions. Its effects are related to its mechanism of action on **neurotransmitter systems**.

**Why the Correct Answer is Right**
Imipramine works by inhibiting the **reuptake of norepinephrine and serotonin**, thus increasing their concentrations in the synaptic cleft. This action is primarily responsible for its antidepressant effects. Imipramine also has **anticholinergic** and **antihistaminic** properties, which can lead to various side effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because imipramine can cause **sedation** due to its antihistaminic properties.
**Option B:** Incorrect as imipramine can lead to **dry mouth** due to its anticholinergic effects.
**Option C:** Incorrect because imipramine can cause **orthostatic hypotension** due to its alpha-adrenergic blocking activity.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that TCAs like imipramine have a narrow **therapeutic index**, making them potentially toxic in overdose.

**Correct Answer:** D. Weight loss