Wellbutrin (bupropion) is a potent inhibitor of the CYP2D6 liver enzyme. Dextromethorphan (the cough supressant) is metabolized by this enzyme. I'm not qualified to give you a detailed analysis, but I can tell you that dextromethorphan and cyp2d6 inhibitors don't mix. A friend of mine taking 300mg Wellbutrin SR drank a 6oz bottle of Robitussin Maximum Strength cough syrup (I wish he'd consulted me, I would have adamantly warned against it!) to experience the PCP-like effects and ended up tripping for THREE DAYS (the effects usually last 8-12 hours). Now, you are taking a normal dose, but it could be enough to produce untoward effects. The sudafed's weak stimulant effect (which I consider to be only slightly weaker than Wellbutrin's, heh) may produce an odd synergy with Wellbutrin as well--some people are stimulated by Sudafed, where I've heard others tell me it makes them spacey and lethargic. Doxylamine may produce drowsiness in a small number of those who take it.