drugs
Historically accepted drugs, such as marijuana, mushrooms, and opium are freely available in many bars and restaurants around town. The majority of bars have 'magic menus' with most of these things on. Consuming these drugs on the premises is fairly safe, although drugs are illegal in Laos and nothing is totally safe.
Southeast Asian 'crystal meth' is known as yabba and is available in both pill and smokeable forms. Formerly legal in Thailand as a way for longhall truck drivers to keep awake. Yabba is an epidemic due to its highly addictive qualities. Manufactured locally, the drug can be cut with any number of substances.
Aside from the drugs already mentioned it is inadvisable to attempt to purchase any other substances not freely available on the 'magic menus' around town. The dangers of most drugs should be well known to travelers, and additionally there is also a police presence. Plain clothed policemen frequently take unsuspecting tourists to the local police station for smoking a joint. The usual outcome of this involves having your passport seized until you cough up a hefty "fine", typically between 3-5 million kip. Once the fine is paid however the matter is generally taken no further and the passport returned; however, the punishment will depend on the officer you are dealing with. Several local policemen are best friends and drinking buddies with restauranteurs who sell opium, mushrooms, cannabis and yaba. Customers are not harassed at these establishments: the police wait until they leave. Some of these same cops own guesthouses near the island. Never surrender your passport if you can help it, and often the best way out of the situation is simply to pay up.
water sports and alcohol do not mix
Drinking alcohol or consuming drugs then entering the water and then swimming or tubing may seem like a great idea but common sense should prevail. If you have been drinking alcohol or consuming drugs do not enter the water. To do so places both yourself and others at risk. Just because a lot of people are doing it does not make it any less dangerous, indeed it probably just enhances the risks.