I sometimes like to smoke marijuana and when i do i usually end up training as i find it helps me to empty my mind. As for drinking, i gave that up as it feels like poison to my body.
Marijuana opens your mind and relaxes the muscles and nerves. It also enhances the senses and improves mental focus. Please take note that i've only listed the positive side effects that happen to me. There are quite a few negative side effects from smoking it too but for me personally i find in small doses on its own (ie no tobacco) it can kickstart an excellent training session.
Many years ago i was a heavy user of the stuff and it had a very negative effect on my body and terrifying effect on my mind and emotions.
My opinion of marijuana is that it's a medicine and can be used but shouldn't be abused.