The Pristiq Secret
Wyeth manufactures both Pristiq and its relative Effexor, one of the most profitable antidepressants currently on the market. Effexor is now available as generic venlafaxine from other manufacturers. Pristiq, on the other hand, remains protected by patent. Because of the patent situation, it is in Wyeth's best financial interest to promote Pristiq as being different from Effexor/venlafaxine. But is it really that different, or is it just the same medication in another form?
This question is surprisingly difficult to answer. Chemically, desvenlafaxine is an active metabolite of venlafaxine. In other words, inside the body, venlafaxine breaks down into desvenlafaxine, and this form of the chemical is effective in the body. The question that must be answered by clinical studies is (a) whether desvenlafaxine is effective as an antidepressant, (b) whether desvenlafaxine is more effective than venlafaxine and other antidepressants, and (c) how the side effects of desvenlafaxine compare to the side effects of other antidepressants.
Many short-term clinical studies have shown that question (a) is true: desvenlafaxine has been proven to be more effective than placebo at improving depression symptoms. Question (b) has not been answered clearly. Desvenlafaxine is good, but is it better than the alternatives? The most recent reports suggest that it is about the same (Clayton et al. 2009; Thase et al. 2009). Some doctors believe that Pristiq is therefore not very useful (for example, Sopko et al. 2008), but others disagree (for example, Kamath & Handratta 2008).
Question (c) may take the longest time to answer, especially in relation to long-term effects. Clinical studies include relatively small numbers of people. Very rare side effects may not show up at all in a clinical study. Typically, very rare side effects of medications are only discovered after the medication has been on the market for some time and many people have tried it.