Combined sales of legal recreational and medical marijuana in the United States is projected to reach more than $8 billion in 2018. That's according to a new report by Marijuana Business Daily citing data from the Marijuana Business Factbook , which forecasts that the 2018 retail marijuana industry could see an estimated $7.4 to $8.2 billion in sales.

The projection is based on sales estimates from the state-legal medical and recreational marijuana markets that already exist, as well as 4-5 additional states that are expected to legalize recreational marijuana and 2-3 states expected to legalize medical marijuana by 2018.

Currently, there are 20 states with legal medical marijuana. Colorado and Washington have both legalized recreational marijuana and about a dozen other states are expected to legalize marijuana in some form in the coming years.

This total is conservative - the reality of retail sales could be larger, Chris Walsh, editor of CannaBusiness Media, the publisher of both the Factbook and Marijuana Business Daily, said in a statement . Nor does it include wholesale cannabis sales, or the billions of dollars in ancillary cannabusiness revenues such as growing equipment, real estate, legal fees, testing labs, paraphernalia, etc.

Walsh's suggestion that sales could exceed that $8 billion mark is supported by another recent study that projects that the U.S. marijuana industry could be worth $10 billion by 2018 .

If Colorado's first two months of legal recreational sales are any sign, the market nationally could see tremendous revenues. In January alone, 59 marijuana dispensaries -- a small fraction of the approximately 550 total dispensaries in the state that could qualify to sell legal cannabis -- generated $14 million in sales . Sales were also up slightly in February, bringing in a two-month total of about $7.6 million in medical and recreational taxes and fees into the state's coffers.