What is the test for establishing a prima facie case in a medical malpractice action?

Mere possibility alone is not sufficient to establish a prima facie case in a medical malpractice action. (Jones v. Ortho Pharmaceutical Corp. (1985) 163 Cal.App.3d 396, 402-403 (Jones).) On this record, the benzodiazepines were not a causal factor in death because the heroin would have caused death regardless of the benzodiazepines. (See id. at pp. 402-403.)

Plaintiff argues there is substantial evidence to allow a jury to infer that absent defendants' breaches of the duty of care in providing psychiatric treatment to Amy, there is a reasonable medical probability that her heroin usage would have remained at a non-lethal level. She points out that a cause of death can be a substantial factor even if not the only factor. (See Bromme v. Pavitt (1992) 5 Cal.App.4th 1487, 1049-1500.)