Alcohol (Beer, Booze, Hooch, Liquor, Wine), 1 hour to perhaps 10 or 12 hours  (Yes, alcohol IS a drug!  Drinking more than "in moderation" can lead to alcohol (drug) abuse...and perhaps alcoholism.  During 2002, more than 18,000 people in the U.S. were killed by too-boozed-up DRUNK drivers!  DON'T BE ONE OF THEM THIS YEAR!)  CLICK HERE for more information about alcohol abuse and alcoholism.
 
Amphetamines (Biphetamine, Black Beauties, Crosses, Dexedrine, Hearts), 1-2 days

Anabolic steroids (Stanzolol, Stanazolol, Nandrolene; Steroids, Roids, Juice),  oral- up to 3 weeks; injected- up to 3-6 months and more

Barbituates (Amytal, Nembutal, Seconal, Phenobarbital; Barbs), 2-3 days

Benzodiazepines (e.g., Ativan, Halcion, Librium, Rohypnol, Valium; Roofies, Tranks, Xanax), 2-3 days

Cocaine (Candy, Coke, Crack, Flake, Rocks, Snow, Whitecoat), (Candy, Coke, Crack, Flake, Rocks, Snow, Whitecoat), 1-2 days

Codeine (e.g., Fiorinal w/codeine, Robitussin A-C, Empirin w/codeine, Tylenol w/codeine, 1-2 days 

GHB (G, Grievous Bodily Harm, Goob, Liquid Ecstasy, Liquid X), 1-2 days

Heroin (Horse, Smack), 1-2 days

Inhalents, just a few hours

Ketamine (K, Kit Kat, Special K, Vitamin K), 2-4 days

LSD (Acid, Blotter, Microdot, Yellow sunshine), a few hours or up to 5 days

Marijuana (Bud, Blunt, Grass, Herb, Pot, Reefer, Sinsemilla, Smoke, Weed), 2-5 days (the daily, heavy user can sometimes be detected up to 30+ days)

MDMA (Ecstasy), 1-5 days

Methadone, 1-7 days

Methamphetamines (Crank, Crystal, Desoxyn, Glass, Ice, Speed), 2-4 days

Methaqualone (Ludes, Quaaludes), 10-15 days

Nicotine (Cigarettes, Cigars, Habitrol patch, Nicorette gum, Nicotrol spray, Prostep patch; Smokeless tobacco, Snuff, Spit tobacco), 1-2 days

Opiates (i.e., Opium: China, Dreams, Laudanum, Paregoric; Dover's Powder), 1-2 days

Oxycodone (OxyContin, Percolone, Roxicodone), 1-2 days