## **Core Concept**
The question tests understanding of the pharmacodynamics of tricyclic antidepressants (TCAs), specifically imipramine, in the treatment of endogenous depression. Imipramine is a TCA that acts by inhibiting the reuptake of serotonin and norepinephrine. The therapeutic effects of antidepressants, including TCAs, typically do not manifest immediately.

## **Why the Correct Answer is Right**
The therapeutic effect of imipramine, like other antidepressants, is not immediate due to the complex neurochemical and physiological changes required for its action. It usually takes several weeks for the full therapeutic effects to become apparent. This delay is thought to be related to the time required for neuroadaptive changes, such as changes in receptor sensitivity and neurotransmitter levels. Specifically, for imipramine, the therapeutic effects are likely to manifest after **2-4 weeks** of treatment.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests a very short time frame for the therapeutic effects to manifest, which is not consistent with the known pharmacodynamics of TCAs.
- **Option B:** This option suggests a slightly longer time frame but still shorter than what is typically observed for the full therapeutic effects of imipramine.
- **Option D:** This option suggests a longer time frame than usually necessary for the therapeutic effects of imipramine to become apparent.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the therapeutic effects of antidepressants, including TCAs like imipramine, typically take **2-4 weeks** to manifest. This delay in action is crucial for managing patient expectations and treatment planning.

## **Correct Answer:** C. 2–4 weeks.