Milosevic died on Saturday of a heart attack in his prison cell near the tribunal in The Hague, Netherlands. He had recently demanded to be temporarily released to go to Moscow for treatment after years of suffering from heart problems and high blood pressure.
But the judges refused, ruling that even with Russian guarantees to send him back to the court, they were afraid he would not return.
The assessment by Donald Uges - based on blood tests carried out in recent months - raised questions about security at the prison and echoed past accusations by the trial's leading attorney that Milosevic repeatedly ignored medical advice and prescribed himself drugs to undermine his war crimes trial.
Uges, the Dutch toxicologist, said on Monday he discovered traces of rifampicin in Milosevic's system - a drug that "makes the liver extremely active" and can undermine the effectiveness of other medication.
Milosevic, 64, had chronic heart problems and high blood pressure.
"First he wasn't taking his medicine. Then he was forced to take it under supervision and his blood pressure still didn't come down," Uges told AP. "So his camp said 'you see, these Dutch doctors don't know how to treat him and he should go to Russia'."
Uges suggested it may have been a ploy to be sent to Russia - where his family was living - for treatment.
Geoffrey Nice, the leading trial attorney in the Milosevic case, had often accused Milosevic of intentionally ignoring the advice of his doctors.
Serbian lawyer shows Milosevic's
letter to Russia before he died
On 1 September 2004, during court hearings, Nice cited four medical reports all supporting assertions that Milosevic was self-medicating - and even lying about his drug intake.
"He has been obtaining for his own purposes other drugs, no doubt to help himself," Nice said. "This material makes it overwhelmingly clear that the accused will do whatever is necessary to serve his own purpose... the court might be quite satisfied he has been manipulating this tribunal."
A second report last August by another doctor working at the UN detention unit identified as Dr Dijkman, said "another drug" had repeatedly been found in Milosevic's blood - a development he characterised as "odd".
Earlier on Monday, Boris Tadic, the Serbian president, said the UN war crimes tribunal was responsible for Milosevic's death, but added that it would not hamper Serbia's future cooperation with the court.
Tadic said: "Undoubtedly, Milosevic had demanded a higher level of health care. That right should have been granted to all war crimes defendants."
"Unfortunately, today we are getting messages from the tribunal that they are not responsible," Tadic said. "I think they are responsible for what happened."
There are fears that Milosevic's
death will fuel Serb nationalism
Tadic, whose Democratic Party led a popular revolt that toppled Milosevic in 2000, said that despite "the lack of credibility" the tribunal has among Serbs, Serbia will try and hand over more war crimes suspects, including top fugitive Ratko Mladic.
Milosevic's death "won't jeopardise our cooperation with the tribunal".
In Moscow, Sergei Lavrov, the Russian foreign minister, said Russia did not fully trust the autopsy on Milosevic and wanted to send its own doctors to examine the body.
Lavrov also repeated Russia's criticism of the UN war crimes tribunal for refusing last month to allow the former Yugoslav president to travel to Moscow for medical treatment.
Clearly stung by the rejection of Russia's "100% state guarantee" that Milosevic would return to finish his trial following treatment, Lavrov said Moscow was "disturbed" by the decision.
"It cannot fail to alarm us that Milosevic died shortly afterwards," he pointedly added.
Lavrov said: "Essentially, they didn't believe Russia. In a situation where we weren't believed, we also have the right not to believe and not to trust those who are conducting this autopsy."
Lavrov said Russia did not fully
trust Milosevic's autopsy
Russia has asked the court to allow its experts to "take part in the autopsy or at least acquaint themselves with its results," Lavrov said, adding that a team of medics was ready to fly "urgently" to The Hague.
The Interfax news agency quoted an unnamed Health Ministry official as saying a Russian team would leave for the Netherlands early on Tuesday.
In another development, Marko Milosevic, Milosevic's son, said the family would consider asking for his father to be interred temporarily in Moscow until a funeral could be held in Belgrade.
Milosevic's lawyer, Zdenko Tomanovic, said Milosevic's body will be claimed by Marko on Monday or Tuesday, .
Although authorities in Belgrade had issued an international arrest warrant for Marko in 2003 for alleged abuse of power, the charges were later dropped.