If you are talking about Cocaine, Ill give you the breakdown from someone who has toked with Jack Herrer, and snorted with Tommy Lee.
Coke being smoked on weed. What a fucking waste, of both. Smoking it that way, has little or no true cocaine effect. It ruins the taste of the weed, definately(makes it taste like burnt plastic etc.), and Cocaine has the opposite effect of weed. So you are just ping ponging yourself. I have had piles of both in the past, it keeps coming up that some one wants a cocopuff, and I oblige them. They all end up agreeing. What a fucking waste of both.
If you want to do coke and weed. Snort coke, and when you need to come down or level out, smoke your weed. Thats it. Don't mix them litterally. Im sure some one, or many people will disagree, I will simply say, WTF. What kind of messed up weed do you have that tastes better with Coke on it?