How long would pristiq (desvenlafaxine) 100 mg take to work after being on 50mg for 5 weeks?

In my experience. Generally about 3-7 days as long as there has been a hint of a response at 50 mg, otherwise it could take up to 14 days if there has been no hint of a response yet. This is my clinical experience. Others may have had different experiences. Best wishes for a quick recovery.
2-4 weeks. Typically should see an improvement in 2 weeks when up titrating the dose but it may take up to 4 weeks in some pts.