DETECTIVES will quiz up tonine doctors they believe could have supplied Whitney Houston with a lethal cocktail of prescription drugs. The superstar singer died in her hotel bath on Saturday after taking a host of powerful sedatives. And last night, sources claimed her drug taking had spiralled out of control in recent months, turning her into a virtual “zombie”. The 48-year-old had become a tortured recluse, regularly spending most of the day in bed before emerging in the evenings to party. Police are now anxious to find out how a recovering crack addict with a long history of drug and alcohol abuse was able to get hold of such a vast quantity of pills. A source said: “The only way Whitney could function was on a cocktail of different drugs – uppers, downers, sleeping pills, painkillers, a whole medicine cabinet. “She was living like a zombie – always on medication. The more she took, the more she needed. “With alcohol in the mix, this was a tragedy waiting to happen. But she needed quite a network to obtain drugs in that kind of number.” Officers will begin their probe at the infamous Mickey Fine pharmacy in Beverly Hills, where Michael Jackson got his prescription drugs. It’s believed at least some of Whitney’s medication was obtained there. Bottles of Lorazepam, Valium and Xanax were found in her suiteat the Beverly Hilton Hotel. All three are used to treat anxiety disorders, while Valium can also ease alcohol withdrawal symptoms and muscle spasms. It’s thought Whitney was also taking painkillers and sleeping pills. Police and the LA county coroner are working on the premise that a combination of drugs and alcohol caused the star to become heavily sedated or overdose – ultimately leading to her death. It’s also possible that she suffered a heart attack caused by an adverse reaction to her medication. An autopsy was performed on Sunday but officials said they wouldn’t have any definitive answers until drug tests are completed in several weeks. Another theory was that the singer took sedatives, fell asleep and drowned in the tub. Police say Whitney was found underwater and unconscious. But the coroner told her family there was not enough water in her lungs to conclude that she had drowned. Detectives are expected to treat the investigation the same way they handled Michael Jackson’s death. They discovered dozens of doctors were supplying the King of Pop with different prescription drugs. Jackson’s personal physician, Conrad Murray – who administered the fatal dose of hospital anaesthetic Propofol – was later found guilty of manslaughter. Yesterday, it emerged that Whitney had visited a doctor at a private clinic in Beverly Hills just two days before she died. US X Factor winner Melanie Amaro revealed that she bumped into Whitney at the surgery on Thursday. Whitney is also known to have visited other private clinics on February 7 and February 2 – and it’s possible that she visited other doctors as well. It’s thought police will also probe whether she used friends, staff or hangers-on to get prescriptions in their own names and then hand over the pills. Detectives are piecing together Whitney’s physical and emotional state before she died. She seemed to have slid back to the days when she and husband Bobby Brown regularly abused drugs and alcohol in week-long party binges. On Thursday night, Whitney looked wild-eyed and dishevelled as she left Hollywood’s Tru nightclub, where she joined revellers at a bash thrown by American singer Kelly Price. She had scratches on her wrist and blood running down a leg and witnesses say she reeked of booze, sweat and cigarettes. Whitney downed tequila at the party and went berserk when she saw her on-off toyboy lover, singer and actor Ray J, 31, talking to another girl. One witness said the former powerhouse vocalist who sold more than 170million albums worldwide seemed “wasted”. A music industry source said: “It looks as though Whitney had got to a stage where she was using Xanax like clockwork. “Mixed with alcohol, it is known to be a killer. It’s the same deadly combination that killed Heath Ledger.”