The spokeswoman for the ICTY, Alexandra Milenov, said on Monday evening that the toxicological examination had not yet been finished and that the first results could be expected later this week.
She declined to comment on statements made by a Dutch toxicologist, Donald Uges, about Milosevic having taken a drug containing rifampicin which negates the effect of high blood pressure treatment.
Milenov only described it as speculation.
"We have no comment on the medications as this is the subject of the ongoing investigation," the ICTY spokeswoman was quoted by the Belgrade-news agency Beta as saying.
She reiterated that preliminary autopsy results showed that the indictee died of a heart attack, adding that one should wait for the results of the toxicological examination.
Asked about the possibility for indictees in the ICTY detention unit to take unprescribed drugs, Milenov explained that guards searched detainees before and after visits, but that visitors were not searched.
Milenov explained that Milosevic had been under the usual regime of supervision and that video cameras had not been used to monitor him, as this measure was taken only when there was reason to believe that a detainee could harm himself or other detainees.
Commenting on reservations expressed by Russian Foreign Minister Sergei Lavrov regarding the autopsy carried out in the Netherlands, the ICTY spokeswoman said that two Serbian pathologists who had attended the procedure at the Dutch Forensic Sciences Institute said that the autopsy had been carried out professionally.