Cincinnati Bengals wide receiver Jerome Simpson (left) is now the target of a massive drug investigation -- after police confiscated a mind-blowing 8.5 POUNDS of marijuana from his Kentucky home.

To put this in perspective -- casual pot smokers typically purchase by the gram ... and there are over 453 grams in a pound.

According to reports, cops searched Simpson's home after snagging a package that was shipped to his house -- containing 2.5 pounds of Mary Jane -- and then found another 6 pounds of weed, packaging materials, scales, and smoking devices.

A rep for the National Marijuana Initiative -- which coordinates marijuana enforcement operations around the country -- believes the house was set up as a "potential distribution network."

Bengals tackle Anthony Collins (right) was also present when police raided the home -- and he's being investigated as well. Police detained the two players during the search, but neither was arrested.