With more than twice as many lobbyists in Washington as Congressmen, the pharmaceutical industry remains America's most profitable, conducting 80 percent of the world's research and development on new drug therapies for everything from the common cold to HIV.

However, a subset of the legal drug industry that requires no research and development beyond undergraduate-level botany -- marijuana -- is growing rapidly into the sort of industry involving serious investor attention. In fact, San Diego-based Medical Marijuana, the industry's largest business, is now worth roughly $200 million, analysts say.

With 16 states and the the District of Columbia legalizing cannabis as a medical treatment, the $1.5 billion legal industry may quadruple to $6 billion by 2018, rivalling the $18 billion illegal pot industry, according to Medical Marijuana Business Daily, a trade publication, and figures from Harvard University economists.

"We're building the first all-inclusive name brand in the cannabis business," said Brendan Kennedy, co-founder of the Seattle-based private equity fund, Prvateer Holdings. "And it doesn't include Bob Marley or the Grateful Dead...."

Many analysts expect the industry to grow and for more doctors to prescribe the drug compound as treatment for medical ailments, as some 52 percent of Americans now support legalizing the drug for not only medical purposes but personal use. However, the industry still has some maturing to do this decade.

"It's not an industry loaded with operating talent," said Josh Rosen, a former Credit Suise stock analyst who runs MC Advisors, based in Phoenix. "But the economics are very similar to other businesses -- you can run a Harvard Business School analysis."

Last week, Rep. Dana Rohrabacher, a republican from California, introduced a bill into Congres that would adjust the Controlled Substances Act to proscribe federal interference with state-level marijuana policy. The House bill, the "Respect State Marijuana Laws Act," would immunize people and businesses from federal prosecution and has two other republican co-sponsors among supporters.