GTFOH! DEMI MOORE IN REHAB FOR HUFFING NITROUS OXIDE!

Demi Moore's friend called paramedics Monday night after the actress inhaled a dangerous amount of nitrous oxide ... TMZ has learned.

Sources tell TMZ ... one of Demi's friends who was at her home told emergency workers Demi was doing whip-its. A whip-it is a street name for a type of nitrous oxide inhalant.

The friend said she became upset when Demi had a reaction to a whip-it and lapsed into semi-consciousness.

It appears Demi had symptoms of a seizure -- after inhaling the nitrous.

A whip-it is not a common drug among people of Demi's age and social status. It's typically used by younger people who are looking for a cheap thrill.

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