Lindsay Clancy Had Several Psychiatric Prescriptions in Her System During Alleged Murder

Shocking testimony in the Lindsay Clancy triple-murder trial ... a forensic toxicologist says she had several medications in her system when she allegedly killed her children and attempted suicide.

Four psychiatric medications were found in Clancy's blood ... two separate antidepressants, a mood stabilizer, and finally, quetiapine -- a drug used to treat schizophrenia, bipolar disorder, and major depressive disorder.

The expert, forensic toxicologist Justin Brower, told the court only one of the four prescriptions was at an elevated level ... that being the quetiapine, but it wasn't at a "toxic concentration" or "suicidal concentration," per The Guardian.

Clancy is accused of strangling Cora, 5, Dawson, 3, and 8-month-old Callan with elastic workout bands at her Duxbury, Massachusetts home.

Lindsay's lawyers are attempting to make a case for insanity, arguing the mom was experiencing postpartum psychosis when she allegedly brutally killed her kids.

Her ex-husband Patrick is helping with that defense.