Demi Moore -- The Drug Emergency 911 Call

TMZ has obtained the 911 call placed moments before Demi Moore was rushed to an L.A. hospital Monday night -- after her friend told paramedics she had inhaled too much nitrous oxide ... aka whip-its.

There is utter confusion at the beginning of the call -- the dispatcher doesn't know which department should handle the call. The woman says Demi smoked something -- not marijuana -- similar to incense and she's having convulsions. The person says Demi was barely conscious.

Capt. Jaime Moore with the L.A. City Fire Dept. tells TMZ ... the FD redacted portions from the tape. Sources in the City Attorney's office tell us references to specific drugs and other substances Demi ingested were redacted because of privacy issues. As TMZ first reported, one of the friends at Demi's house told paramedics she has been using whip-its -- nitrous oxide.

The person says she's been taking some other stuff recently but she didn't know what it was ... and she was having "issues" lately.