Well, I think it largely depends upon the meds, so I'll let our pharmacology expert answer that part.

But I can say that my husband usually experiences withdrawal effects (irritability and less sleep, mostly) within a few days of forgetting to refill his escitalopram prescription, and the effects can indeed last a few weeks. I was on it for a few months myself, and weaned off slowly without bad effects, but the sleeping less was a benefit in my case, not a disadvantage because the meds made me exhausted.

Hopefully Jerry or Larry Hoover will be by soon to answer your question. Good luck!