Usually 3-4 weeks for all MAOIs. But there is always some variability, plus who knows. It may be a gradual onset of action instead of sudden. I read about a mechanism of action for MAOIs being the eventual regulation of some neurotransmitter receptors, which can take 2 weeks, once MAO is inhibited.
You might need a higher dose, too. How much are you taking right now? IMO if you didn't respond at the 45 mg at 4 weeks, try 60 for 2 weeks.
Medication-related posts are for brainstorming purposes only. Talk to your doctor.
My meds: Parnate, Lamictal, Wellbutrin, trazodone