This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Psychiatry
Sudden discontinuation of which of the following drugs can cause agitation, anxiety and insomnia? 
Select and explain. 
A. Imipramine, B. Valproate, C. Olanzapine, D. Venlafaxine
D: Venlafaxine
Answer: D: Venlafaxine 
Explanation: Venlafaxine is the most common drug associated with discontinuation syndrome.