I've seen a few posts recently on marijuana, mostly in support of it's use. So I thought I'd put this here;
First, unless your growing this stuff yourself, you've no idea what else is in it, so "safe" is a relative term.
Second, yes, of all the drugs, cannabis is the safest. Very few addiction issues, and if smoked through a water filter, fairly easy on the lungs (although even that only goes so far).
BUT, there are long term physiological/psychological effects that come from smoking weed. And while you can lead a fairly happy life doing it regularly...
Your memory centers will be effected. Your physical reflexes will be slightly slower. And your ability to learn and process logical thought will suffer too. In essence, you'll be compromising your potential as a human being.
Which is fine. The world needs ditch diggers too.
Most importantly will stunt your growth into emotionally maturity (hard even without weed!)
Every experience, every happiness, every pain and loss will be blunted by the "high" you live in. If you do finally stop, you'll find dealing with your emotions in the "real" world difficult. You'll feel raw to every insult, every difficulty. Your emotional maturity will be of essentially of an age right when you started habitual use in terms of coping skills.
So... try to get over it. I'm not saying run down to your local NA (unless you need to) perhaps consider a little restraint. I've dealt with long time marijuana users in counseling, and they always feel like something insidious has happened to them. Like they're a "lesser copy" of themselves. They say it's very subtle, almost unnoticeable, which for them, makes it worse. Like they can almost reach the cookie jar, but...
You can recover from this state. It takes up to a year or two, but it does get better. *shrug* Unless you don't mind. Which many don't.
If you've been doing it more than once a week, for some time, you SHOULD be concerned about the above.