Anna Nicole Smith's son died from methadone and antidepressants

SAN JUAN, Puerto Rico – Anna Nicole Smith's 20-year-old son died from the accidental effect of methadone and two antidepressant drugs interacting in his system, according to a prominent American pathologist who conducted a private autopsy.

The low levels of the three drugs detected by toxicology tests indicated Daniel Smith died "a tragic, accidental, drug-related death," Dr. Cyril Wecht told The Associated Press on Wednesday.

Smith died Sept. 10 at his mother's hospital bedside in the Bahamas, where the reality TV star and former Playboy playmate was recuperating from giving birth to a daughter three days earlier.

Wecht said Zoloft, Lexapro and methadone had a lethal "cumulative effect on the central nervous system" that ultimately stopped Smith's heart — a "classical" death resulting from a combination of drugs without an overdose of any one.

"Oh my, that's a really lethal combination right there," said Lisa Johnson, a pharmacist at Cedars-Sinai Medical Center in Los Angeles. "If that's what he was on, it could very well have caused this."

"The methadone will slow you down, but the other ones make your system speed up, so it's an odd combination," she said in an interview.

Smith had reportedly been suffering depression related to a breakup with a girlfriend when he went to visit his mother and newborn half-sister in Nassau. Zoloft and Lexapro, which a U.S. doctor had prescribed, are antidepressants commonly used to treat anxiety and panic disorders.

Wecht said he did not know why Smith was taking methadone, a pain-reliever that is also used to ease heroin cravings for recovering addicts.

"It is used for people who have been on heroin or morphine," Wecht said from his home in the Pittsburgh area. "I have made those inquiries. I can only say to you no one has suggested anything having to do with drug addiction in this boy."

A lawyer for Anna Nicole Smith said she hired Wecht, a forensic pathologist who gained fame as a consultant on celebrity cases including Elvis Presley's death, to end speculation about her son's death.

He conducted the autopsy Sept. 17 at a downtown Nassau morgue, and signed a death certificate with the official pathologist that listed the cause as pending toxicology reports. He had previously ruled out the possibility of suicide or homicide.

Wecht said he would share his results Thursday with the examiner who conducted the official autopsy, but did not know whether they would issue a joint report on the cause.

In Nassau, Chief Magistrate Roger Gomez said he has not yet received official toxicology results, which will determine whether a jury inquest into the death is necessary. He declined to comment on Wecht's findings.

Smith's body on Wednesday remained at a Bahamas funeral home hired by the family.

Howard K. Stern, a lawyer for Anna Nicole Smith who was in the hospital room when Daniel died, told CNN's "Larry King Live" on Tuesday that he is the father of the 3-week-old baby girl, Dannie Lynn Hope.

But photographer Larry Birkhead, a former boyfriend of Anna Nicole Smith, told Us Weekly magazine that he's the father and is seeking a DNA test to prove it.

Stern said he plans to marry the 38-year-old celebrity "at some point."

"Right now we have to somehow get through what we're going through," said Stern, adding: "And I'll tell you, our baby is the one ray of hope."

Daniel Smith, who appeared several times on the E! reality series "The Anna Nicole Show," was the son of Anna Nicole and Bill Smith, who married in 1985 and divorced two years later.

Anna Nicole married Texas oil tycoon J. Howard Marshall II in 1994, when she was 26 and he was 89. He died the following year and she has since been involved in legal disputes over the estate.

Associated Press writer Jessica Robertson in Nassau, Bahamas, contributed to this report.