A mentally disturbed Singaporean student who poisoned her classmates has been expelled from the Stanford University, a media report said on Thursday.

Ouyang Xiangyu, 26, was charged in California with four counts of poisoning the drinking water of two of her lab mates between September and November last year. She was initially only banned from campus.

Stanford University authorities confirmed to The Straits Times that she has been officially expelled.

Ouyang admitted to adding paraformaldehyde (PFA) to two water bottles that were not her own but is likely to plead not guilty due to mental disorder.

Earlier, she had sabotaged her lab mate’s experiments starting from mid-August. Ouyang is currently on a $50,000 bail and is barred from leaving the US.

According to California law, she could face between two and five years in jail if found guilty. And another three years could be added if the poison involved causes "great bodily harm or death".