Smith died of a drug overdose on Feb. 8, 2007, in a Florida hotel room. Prosecutors call Stern an aider and abettor of two doctors, Dr. Sandeep Kapoor and Dr. Khristine Eroshevich, who are charged with improperly prescribing the drugs that killed Smith.
All three pleaded not guilty in May to conspiring to illegally provide Smith with controlled substances. They re-entered their pleas Wednesday to the amended complaint.
The doctors each face six counts including conspiracy, and up to five years, eight months in prison if convicted. It was not clear what sentence Stern would face if convicted, Los Angeles County district attorney's spokeswoman Jane Robison said.
Search warrant affidavits suggest Stern put his name on prescriptions for opiates that were given to Smith, and claim that 44 different medications were prescribed for Smith under a number of other names, including Stern's.
Outside court, Stern's attorney said the additional charges were filed because prosecutors realized their case against him was weak.
"They are using a shotgun approach," Steve Sadow said. "They are throwing everything at him to see what sticks, and nothing will stick."
Prosecutors declined to elaborate on what prompted the additional charges against Stern.
Sadow argues his client should not be blamed for Smith's death because Stern was relying on the doctors to treat the former model, who he said was recovering from an illness at the time of her death.
"Anna Nicole was a very strong-willed woman," Sadow said. "She took the prescription medications because she thought it was in her best interest to control her pain.
A preliminary hearing is set for Oct. 5 but prosecutors asked for a delay until Oct. 13. A decision will be made following a scheduling hearing Oct. 1.
On Tuesday, Kapoor's attorney said she was outraged by claims in search warrant affidavits that her client crossed professional boundaries and had a sexual relationship with Smith.
Attorney Ellyn Garafalo told The Associated Press that Kapoor is openly gay and never had a sexual or social relationship with his famous client.
A picture of Smith and Kapoor that was cited in the affidavits was taken at a gay pride celebration they both attended, Garafalo said.
"These search warrant affidavits are based on insufficient information and they are wrong in material respects," Garafalo said in an interview with the AP. "The prime example is that Dr. Kapoor is openly gay and never slept with Anna Nicole Smith or any other woman."
Garafalo said the doctor and patient encountered each other in a bar after a gay pride parade, but did not have an ongoing social relationship.
District attorney spokeswoman Sandi Gibbons declined comment saying, "The case has not yet gone to preliminary hearing and it would be inappropriate for us to be making comments outside court."
Eroshevich, a psychiatrist, also is accused of an improper sexual relationship with the former Playboy model based on photographs found on a computer of the two women naked together in a bathtub "in various intimate embraces."
Eroshevich's lawyer, Adam Braun, declined to comment directly on the pictures but said that the relationship between Smith and the psychiatrist began as one of friendship and evolved into a patient-doctor relationship.