Media reports Monday said Moore, 49, was rushed to a Los Angeles-area hospital and treated for an undisclosed illness.
Her publicist Tuesday issued a statement saying she was seeking treatment for exhaustion and would not be playing a supporting role in "Lovelace" as planned.
TMZ said late Wednesday Moore's friends called paramedics Monday night because they believed the "A Few Good Men," "Ghost" and "About Last Night" actress inhaled a dangerous amount of nitrous oxide while "doing whip-its" and appeared to be having a seizure.
"Whip-it" is a slang name for a type of inexpensive nitrous oxide inhalant found in small metal canisters used for recharging whipping cream cans. It is most commonly abused by youths.
Moore and actor Ashton Kutcher announced in November they were ending their six-year marriage.