Some UK slang I've encountered, some are pretty funny;
Amphetamine - speed, whizz, fast, billy, phet
Ketamine - wonk, wobble, wob(s), katie, kevin, katheryn, horse, pony, donkey dust, grand national, k, kellogs, breakfast, cereal, hippy smack
Heroin - smack, bobby, brown, dark, gear, h, dope
Cocaine - charlie, charles, posh, white, sniff, yay, yayo, top/top shelf, chicken salad, fuel, power, 100mph
Crack - light, stone, pebs, rocks, stalone, hard food
Diazepam - blues, vallies, vals, valerie, sleeps/sleepers, downs
Weed - zoot, mary, mary-jane, green, stink, smoke, dutch/dutchie
Pregabalin - pg tips, peegees, pregabs, gabs, gabby, gabbo
Acid - trips, tabs, sid, sidney, liquid, drops
Mephedrone - plant/plant food, drone, meow/meow-meow, bubble, m-cat, cat, cat food, sparkle
MDMA - mandy, madman, molly recently, m-d, mud, boots
Ecstasy pills - pingers/pings, gurners/gurns, churners, sweets, littles, little ones, disco biscuits
Nitrous - hippy crack, nos, balloons
There's loads more, can't think of them all atm