Pristiq (desvenlafaxine) typically starts to work within 1 to 2 weeks, but it may take 4 to 8 weeks to feel the full benefits. Some people might notice improvement in their symptoms like mood, sleep, and appetite within the first couple of weeks, but it’s important to continue taking it as prescribed, even if you don’t feel better right away. Everyone’s response to the medication can vary. If there’s no improvement after a few weeks, consult your doctor.