Former A*Star scholarship holder Ouyang Xiangyu, 26, has pleaded "no contest" to four felony counts of poisoning, according to the Santa Clara County District Attorney's office.
The former Stanford University graduate student entered the plea on Tuesday at the Palo Alto Courthouse in California and could face a sentence of up to one year in a county jail. She had pleaded not guilty in May.
A plea of no contest has the same effect on a criminal sentence as a guilty plea, but may not be taken as an admission of guilt for any other purpose, according to the California Courts website.
In Ouyang's case, had she not pleaded no contest, her maximum punishment could have included one year in the county jail and three years of formal probation, restitution, fines and fees, according to deputy district attorney Anne Seery.
She was arrested on Nov 16 last year for poisoning the drinking water of two Stanford laboratory mates between September and November last year.
The lab mates said they experienced a burning sensation in their throats after drinking from their bottles, but there was no serious injury.
Ms Seery told The Straits Times: "We may never know why she did this, but this was dangerous conduct. Thankfully, at the end of the day, no one was seriously hurt."
When questioned by the police in November last year, Ouyang said she had been experiencing severe insomnia and dizziness since September and also admitted to putting paraformaldehyde in two water bottles belonging to others in her lab.
She had also sought the help of a psychiatrist at the time.
According to court documents, Ouyang said she never had any intention of harming anyone.
Other Stanford students who spoke to The Straits Times and knew Ouyang said she was a quiet and shy individual and had seemed stressed by school work.
Ouyang, who has since been expelled from Stanford University, is also accused of sabotaging a lab mate's experiments from mid-August last year.
Ms Seery said a stay-away order from Stanford is in place and Ouyang is to have no contact with any of the victims.
Ms Lisa Lapin, associate vice- president for communications at Stanford University, said: "This was a serious matter that the university addressed swiftly and reported to law enforcement.
"We are appreciative for all concerned that the judicial process is concluding and that everyone who was involved can move beyond this distressing episode."
Sentencing is scheduled for Jan 15 next year. Ouyang and her lawyer could not be reached for comment.