A source told CNN that the singer was seen ordering and drinking a lot of alcohol at the Beverly Hilton just days before she died.
Houston ordered the drinks before 10 a.m. last Wednesday and Thursday. She allegedly complained that the drinks were watered down.
Meanwhile, more details are being released about Houston's funeral plans.
A television camera will be allowed inside the New Jersey church so that fans can watch the private ceremony live online.
Houston's funeral will be at New Hope Baptist Church, where she sang as a child. Afterward, Houston will be buried in Fair View Cemetery in Westfield, N.J., according to her death certificate. Her father, John Russell Houston Jr., was buried there in 2003.
Officials have not said what medications they have recovered from Houston's room at the Beverly Hilton Hotel. The singer was found underwater in a bathtub by a member of her staff hours before she planned to attend a pre-Grammy gala.
Police have said there were no signs of foul play and there were no signs of trauma on her body when an autopsy was conducted on Sunday.
It will be weeks before toxicology results reveal the medications and quantities, if any, that were in Houston's system when she died. Her history of substance abuse has added to the speculation that her death may have been caused by prescription drugs.
The Associated Press contributed to this report.