Cigarettes: Absolutely ok to smoke, anywhere u want. People in Thailand are very tolerant of a lot of things we forigners do(within reason, of course. Some things they find just too offensive), even if they do not do these things themselves. Cant remember how much cigarettes cost, in Thailand. I used to smoke, in bars and cafes, all the time, when i was there
Marijuana: Highly illegal. Not advisable to smoke it anywhere. However, people often smoke it, in guesthouses. Fines or jail sentences apply to marijuana use, in a lot of asian countries. Look up internet for specific laws, in Thailand.