For heavens sake, stop wondering, thinking about your friends way of using it, and nevere think the way your thinking right now. It's obvious by your E-tone(TM): The curiousity which has a force behind it and the kind where in the back of your mind, you might do it. Face it dude, you knew what kind of answers you were going to hear when you started this thread.
And yes, our priority above all else is HR. But I myself and most will tell you what you want to know, but give you serious reasons to consider before making a choice from which there is no going back.
What does it feel like? There's nothing to compare it to, and there is nothing that feels as good as IV cocaine. Except I like about 3:1 coke/dope and because I've gotten so sick of poking myself hours later when I'm dehydrated and struggling to find a vein, risking a miss- I've gotten to where I do very large shots so that my quantity will run out quickly. You know it's coming when the instant you begin pushing the plunger you smell/taste and sense ether or acetone, or whatever solvent and then it reaches your lungs and as this is registering...Magic. Everything sounds metallic, vision becomes fluttery. But it's purely the dopamine and norepinephrine flood that is like you having had a Ferrari for ten years, but you've only been allowed to go 70mph. There is a governor which restricts you. One day you pay a guy and he takes that governor off and you take it on a closed racetrack maxing out around 185. It's incredible. You want to do it again but the governors been reinstalled. Shit you want to do it again. And you want it now. Extrapolate this metaphor into your life, but increase the neurophysiological reward by thousand. But also know you've made a decision which has given you knowledge some would pay not to have or get rid of, which you can never un-know.
If you've really not snorted it, then why ask about IV effects here? No one will tell you to go ahead and sniff some and then shoot it. I recommend never trying cocaine if you haven't yet, and perhaps consider avoiding those friends when they are using IV drugs. Because Exposure+Time and your already potentially dangerous curiousity= Eventually and inevitably giving in.
Cap'n- you throw up everytime you push with coke? Holy shit that's gotta suck. I hear people complain about how the nausea is so bad that aspect is literally an additional contingency whpich requires consideration and planning. I think about how many I've done in the car, plenty in parking lots with cops 50 yds behind me, oblivious, talking about what their gonna do with their families when vacation comes. If I were to lean out my door and throw up, that would be bad. I suppose I have to have some kind of puke container.