Los Angeles (AFP) – As pot smokers prepare to light up for “4/20” — the annual counter-cultural celebration of cannabis held on April 20 — the United States’ legalization experiment blazes ahead. Here are five things to know about marijuana in America: Where is it legal? – Eighteen of the 50 US states, plus the capital Washington, have so far legalized recreational weed use for adults. Most states allow at least some medical use — ranging from oils with low levels of the active ingredient THC to near-legalization. Just a few conservative states such as Idaho, Wyoming and Nebraska have held …