^ don't use vinegar. It's fucking awful for your veins. Same with lemon juice, which can have bacteria. Vitamin C does work because it IS acid, but you need straight ascorbic acid, not a drink mix. You can usually find it in the vitamin aisle.
It's been my experience that it's much easier in your veins just to use powder cocaine. And even though using ascorbic acid technically converts crack cocaine back to cocaine, I noticed the difference vs powder cocaine that was never cooked into crack. Shooting crack was like a kick in the chest and nauseating while also feeling good at the same time. Powder lasted longer and just felt good without feeling like I was getting hit by a train.