Even if California's Prop 19 passes on November 2, there are still other hurdles to the business of marijuana standing between investors and their returns.

"Right now the medical cannabis industry is sexy," according to Steph Sherer, a medical marijuana patient and founder of Americans for Safe Access. "But if you talk to people in this industry, they are broke, overtaxed and overregulated. The market isn't growing as fast as the industry is growing."

But It isn't just government holding the industry back. It's banks too.

Jill Lamoureux, the owner of a Colorado medical marijuana dispensary, said her business has been kicked out of three different banks. And Wells Fargo, one of the few banks that was accepting medical marijuana dispensary accounts, will no longer accept any cannabis dispensary clients. When Justin Hartfield called to find out why, he was told it wasn't in the bank's best interest since dispensaries didn't take out mortgages or loans.

Hartfield is the co-founder of Weedmaps.com, a database of medical marijuana dispensaries, which is why he has such a vested interest in dispensaries' relationships with banks. The site– what Hartfield calls the first social media website for medical marijuana patients, bought an ISO (independent sales organization) to provide credit card swiping machines at the dispensaries.

But Visa and Mastercard are fickle about their policy on medical marijuana and some transactions were allowed while others were arbitrarily rejected.

One way out, according to Hartfield: buy the bank.

"A marijuana branded bank is just what the doctor ordered. If we provided a bank, I think the market could be expanding at a much higher growth rate."