It took me nearly 2 years to convince my mom that smoking weed doesn't impact my life in a negative way. A lot of information and learning went in on her part. At first she was devastated, she is a very worrying mother. Now that I am older and living on my own, that doesn't matter, but I try to keep a close relationship to my parents and be open about my everyday life.
If you feel the need to tell them, do so, but be prepared to be greeted with hesitation and consequences. Or you could hide it from them like most pot smokers. They won't ever agree to it, but they may come to accept it if you can show them you are responsible.
^ This pretty much.
My mother knows everything to do, it bothers her, but it's a good way for me to show her not to worry so much. That I can do drugs and still go to Uni, and do everything I need to do. As a result of being open with her, and her being accepting of my behaviour, we have a better relationship than ever.
She doesn't use any drugs, but I'll still smoke a few bongs out the back in her company, or even tell her "By the way, I was planning on dropping some acid in like an hour" although she's not so tolerant of the latter, as she doesn't really understand much about it. I've pulled back from unnecessarily discussing the things she doesn't understand, it has the opposite effect and makes her worry more.
I consider it as mutual respect, she knows when I'm doing the drugs, exactly what I'm doing and when, so she doesn't have to imagine me shooting smack somewhere in an alley and give herself a heart attack, and in return she doesn't make my life unnecessarily difficult for choosing to use drugs.
My Dad however, used to use all these drugs and then some, and in fear of me making the same mistakes he did adopts a very different attitude, and unfortunately this has just made our relationship far more strained (OOoh get it?!)8)}
I guess the point is, everyone's parents are totally different. You have do what's right for your parents. I used to stock up on very large amounts of weed, but when the 4 ounces of Jack Herer I had stunk my whole fucking house out, and I mean every square inch of it, I learned there were indeed limits to how far I could push my somewhat drug use tolerant family.
Funnily enough through experimentation with psychedelics I was able to come to the conclusion, that my behavior and choices impacts my parents as well, and I'm not the only person in the house whose opinions matters. Sometimes you have to put your own thoughts and feelings aside to see the big picture, especially when you're a teenager and your whole life revolves around yourself, and establishing your identity within this big bad world.
You need some sort of mutual respect OP, perhaps you can respect your parents wishes to not smoke in their house, but at the same time politely ask them to explain why they feel so strongly about it, and perhaps have an adult discussion about the issue. Once my parents got over the shock horror of my baby is on drugs, we were able to discuss it like human beings instead of emotionally rabid animals.