products used in the cultivation of indoor plants -- and a subsidiary of OTC stock Terra Tech /quotes/zigman/8701126 /quotes/nls/trtc TRTC +1.19% . "The industry is expanding, and there are all kinds of investment opportunities." For regular investors looking to get in on the action -- and without having to actually grow or sell drugs -- there are several small-cap stocks that stand to gain from marijuana's growing acceptance. Medbox /quotes/zigman/7157004 /quotes/nls/mdbx MDBX -90.24% , an OTC stock with a $45 million market cap, for example, sells its patented dispensing machines to licensed medical-marijuana dispensaries. The machines, which dispense set doses of the drug, after verifying patients' identities via fingerprint, could potentially be used in ordinary drugstores too, says Medbox founder Vincent Mehdizadeh. Based in Hollywood, Calif., the company already has 130 machines in the field, and it expects to install an additional 40 in the next quarter. "The smart money is trying to help with compliance and transparency," Mehdizadeh says. Expelled U.S. Olympian: Yeah, I ate marijuana Nicholas Delpopolo becomes the first U.S. Olympian in London to be disqualified for failing a drug test. Of course, investing in drugs the federal government still outlaws poses enormous risks to investors, says Sam Kamin, a law professor and the director of the Constitutional Rights & Remedies Program at the University of Denver. In fact, nearly 500 of the estimated 3,000 dispensaries nationwide have either been closed by the federal government or shut down in the past year, says a spokesman for StickyGuide.com