While there is a placebo effect, when it comes to substances like cannabis you can experience serious temporary mind alteration if you consume enough, to a degree that is far more than a placebo ever could. Just like alcohol if you drink enough of it.

So, I disagree with you quite a bit here. Your mind will pump out ideas at a much faster rate when you consume a sufficient quantity of cannabis. Many of these ideas may be awful, but it's an experience shared by millions of people. Your mind begins to freely associate things haphazardly.