Charlie Sheen had a "briefcase full of cocaine" delivered to his home -- and was using large amounts of the drug during the 36-hour bender that landed him in the hospital ... this according to a source inside the house.

We're told Sheen had several people inside his home during the 36-hour span that started Tuesday night -- including 2 porn stars, a business associate, and several other women.

After hours of drinking, we're told a person showed up to the house with a designer "briefcase" -- that contained multiple "bricks" of cocaine.

We're told Sheen immediately began doing the drug for several hours.

Sheen was eventually hospitalized early Thursday morning for "severe abdominal pain."