Some kids experiment, some make lifestyle choices that I agree with and some that I do not. Some make lifestyle choices that are dangerous to health and some are innocuous. I would MUCH rather my teen smoke pot than drink alcohol. I would much rather my teen smoke pot than smoke cigarettes. People don't die from smoking pot, the same cannot be said for alcohol, cigarettes, narcotics, prescription drugs, cocaine, meth amphetamines etc... (And before someone says that smoking pot increases the chance of getting lung cancer, the most recent studies show the opposite http://www.webmd.com/lung-cancer/new...to-lung-cancer
.) In other words, all drugs are not equal, most teenagers know this and think that adults are naive, ill informed or both if they present "drugs" as a monolithic problem.
As a high school teacher and a parent, I can say that I have seen teenagers have the genetic addictive tendencies mentioned by elsie123 and have a very difficult time taking care of their responsibilities in school. These kids cannot smoke pot and lead normal lives effectively. They have a problem and need to stop; and this problem will exist regardless of their drug of choice. I have also seen teenagers smoke pot daily and have it not interfere one iota with their academic abilities and get into top schools like Brown and Harvard. I can't say the same thing about those drugs mentioned above as they cause greater problems even in the kids without the addictive personalities. Each kid is different, and predicting whether smoking pot will be a problem or not doesn't do any kid any good. Open communication is the key. If you have rules in your home, make them known. If you live in a state that criminalizes marijuana, there are legal risks that obviously need discussion. To the OP; once you determine exactly what your objection is, it will be easier to have the discussion.