You may have heard about the enormous gains marijuana stocks have generated over the past couple of years. You might also be aware of predictions about how large the marijuana industry could become, including a recent projection that the U.S. marijuana market could more than triple, reaching $22 billion by 2022. Many companies in the cannabis industry have opted to go public, making their shares available for purchase on public stock markets, to raise cash to fuel additional growth. But there remain two fundamental arguments against investing in marijuana stocks. One is the risk that the projected growth won't materialize – it remains illegal! Another is that marijuana companies' growth potential may already be reflected in their stocks' high valuations.