Her fatal dose was administered by a fLeets enema. Read "Goddess" which came out in the 70s or early 80s. Absolute, direct link to RFK.
I'm familiar with the book Goddess and not persuaded by its argument. Having written true crime books myself, I know its easy to stretch the facts a bit and -- voila! -- rank speculation comes out sounding like the only possible interpretation.
I don't doubt that RFK was involved somehow. But neither do I buy the story that he and Lawford personally visited Marilyn's home that night.