Ever since i started 225mg effexor (venlafaxine) i pee frequently and lost 5lbs of what appears to be water weight. is this possible?

Possible. : It is possible that Effexor (venlafaxine) is causing increased urinary frequency. However, the chance of this is less than 1%; it is a rare side effect. The more likely causes may be too much caffeine + water, general anxiety (high doses of Effexor (venlafaxine) can make anxiety worse at at first, which triggers the urge to urinate. Finally, if you are sexually active, , consider a urinary tract infection.