Dexter makes some "knockoff" cocaine for Debra's party by grinding up caffeine and benzocaine tablets. Benzocaine is a synthetic, amino ester-class local anesthetic, typically used as a topical anesthetic, it is in the same class of drug as anesthetics like novocaine and lidocaine; benzocaine is the active ingredient in many over-the-counter anesthetic ointments, such as products for oral ulcers, or ear drops for ear aches. Cocaine is also a ester-class anesthetic, while also possessing narcotic properties, it has been used in medicine for hundreds of years to numb skin prior to surgery, especially in the mouth, nose and eyes, it's sometimes still used in modern medicine for this purpose because it also has strong blood clotting factors and helps control bleeding during mouth, throat and nose surgery. Novocaine, in the form of procaine, was actually synthesized from cocaine (hence the similar name), after chemists experimented with ways to create a local anesthetic drug without cocaine's narcotic effects.
Synthetic anesthetics like benzocaine don't produce a narcotic effect and can't get you high, although snorting it would numb the inside of the nose the way cocaine does. The increased heart rate and heightened energy levels of snorting powdered caffeine, combined with the placebo effect, might mimic some of the effects of cocaine enough to trick teenagers who've never actually used cocaine, although it wouldn't fool someone who has used cocaine before.
