This year's 4/20 rallies came the day before a prominent pot legalization group holds is annual convention in Denver.
9Health Reporter Dr. John Torres says the long-term effects of smoking marijuana aren't yet clear.
"Some studies have shown that it causes some problems in the lungs. It can cause cancers and other long-term issues like COPD or emphysema. Other studies have not shown that. And again, this is one of those things that's very controversial," Dr. John said.
Dr. John says, in his professional opinion, it's not good to put anything foreign into your lungs.
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