Heroin addict Kathleen McCluskey, 42, of Cambridge, was cleared of two counts of murder but convicted of two counts of manslaughter by a jury at Norwich Crown Court.
McCluskey was also cleared of an allegation of administering a drug to a third man.
Last week McCluskey, who is unemployed, was found not guilty of murdering two other men, one of them her husband, by helping or administering drugs overdoses.
Judge Justice Moses ordered jurors to bring in not guilty verdicts on those two charges after ruling that prosecutors had presented insufficient evidence.
The judge yesterday adjourned sentencing on the manslaughter convictions until next month.
He said he wanted specialist reports on McCluskey's psychiatric state after being told that she had a history of mental health problems.
McCluskey, who had denied any wrongdoing, was remanded in custody pending sentence. As she was led away from the dock, she shouted: "Ignorant bastards."
All of the alleged victims were known to McCluskey and lived near her in Cambridge. All had histories of drug or alcohol problems.
Police investigated all four deaths separately but a prosecution was only launched following the fourth death.
Detectives could find no evidence of a motive for murder although their inquiries established that McCluskey had been present at all four deaths.
"This was a complicated case and a very unusual one," said Detective Chief Inspector Paul Craig after the verdict.
"The common thread was that she was present at all four deaths. That seemed to be too much of a coincidence. We found no evidence of any obvious motive.
"It was a case in which we and the lawyers felt that a jury should look at the facts and decide. I respect the decision they have come to."
McCluskey was convicted of the manslaughter of artist Mohammed Assadi, 47, who died in Cambridge in August 1999.
Tests show that the cause of death was an overdose of the heroin substitute, methadone. She was also convicted of the manslaughter of Marvin Brodie, 32. Brodie was a care assistant who died in Cambridge in June 2000.
Tests showed he died as a result of methadone intoxication.
She was found not guilty of killing Raymond Diaz, a 50-year-old unemployed man who died in Cambridge in March 2001. Tests showed that he had died from drug poisoning.
She was also cleared of killing her second husband James McCluskey, 44. McCluskey, who was unemployed, died in September 2001 as a result of drug poisoning.
Jurors cleared her of administering a noxious substance, methadone, to Peter Bakulinskyj, 38, in Cambridge in December 1999.
Detectives suspected that McCluskey's first husband James Baxter might have been involved in the deaths of Assadi and Brodie.
They established that he had been present although they could find no evidence that he had committed an offence.
Officers were unable to follow up investigations into Baxter because he committed suicide while depressed in January 2001 aged 50.