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There are several potential adverse effects with an increase in venlafaxine, which can include: anxiety, panic attack, agitation, trouble sleeping, irritability, impulsivieness, restlessness, changes in mood.
Given that this is a one time issue, these are unlikely. And, given the time between doses (a.m. and p.m.), and the fact that it is extended-release, I would not expect any of the above to be of major concern. Most of the drug is excreted in the urine within 48 hrs. And so, I would not anticipate any longer term worries either.
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