It’s a cliché that there are two reasons why foreigners come to Cambodia, Angkor Wat and Lawlessness. There is certainly more than a grain of truth to this. In Cambodia, virtually anything is for sale, and drugs are certainly no exception. Serendipity Beach in Sihanoukville and the Lakeside (Boeng Kak) of Phnom Penh are the main places to indulge in drugs in Cambodia. Virtually everything imaginable is available, with the possible exception of mescaline and cocaine (the latter is available, but extremely expensive and of reportedly low quality).
Cambodia is a psychedelic place without any drugs, but dabbling in psychotropic substances makes it all that much weirder. Be careful not to overdo it, though, or you’ll end up like all the other hollow-eyed weirdoes around. You’ll see them when you get there…
Marijuana is the drug of choice for the traveler in Cambodia. It is readily available, quite good by SE Asian standards, and cheap. Ten grams of “skunk” (decent, seedless, but un-manicured buds…) will cost about $8-$10. The quality is higher at the end of the wet season. Police don’t give a damn about travelers smoking anywhere, so treat joints like cigarettes and you’ll have no problems. No one ever gets in trouble for having weed.
Opium is also available, as is everything else imaginable. Try to limit drug intake if you want to keep your head together. Remember: everything can go wrong in Cambodia if you lose your head.