Why is effexor officially indicated for anxiety, but pristiq (desvenlafaxine) only used off label for it? seems strange given their relation.

Pristiq (desvenlafaxine) is newer: Effexor and Pristiq (desvenlafaxine) do work in the same way, Pristiq (desvenlafaxine) is simply the active metabolite of Effexor. The answer is that Effexor has been out much longer than Pristiq (desvenlafaxine). Drug companies must demonstrate effectiveness for different indications through expensive clinical trials to get FDA approval for that condition. If Pristiq (desvenlafaxine) is proven to be effective for anxiety, FDA will approve it for that indication.

Agree w Dr Guerra: In order to have an FDA indication , the drug must have been specifically tested for that condition. Pristiq is newer to the market.