We already know that Murray wasn't really treating insomnia so we can get that out of the way.
We know that Murray was given Michael general anesthesia levels of propofol so we have to look at it from that point-of-view. When we do, it seems like the 40mg isn't that high of a number and like Anderson said it is high therapeutic. No one believes that the Lorazepam was unnaturally high and Shafer, who knows more about these drugs than both of us combine, didn't say anything about it being outraged or unheard of.
Also Shafer never said Murray gave it as a continue dip. He said that Murray gave Michael an injection of Lorazepam every half of hour from midnight to around six. Which from my understand is common in anesthesia, which was basically what Murray was doing on the 25th.
Finally cinzia, yes it's juvenile to us for a doctor to blame a patient, but not everyone sees it that way. Another example, Elvis literally did have a doctor feeding him drugs in his house and he was left blameless, even now, because the general thinking is that Elvis was an addict and he would had gotten drugs regardless if that doctor helped him or not. Also for the record, Anna Nicole Smith's doctors and boyfriend were with her when she died. They knew she wasn't well, but the kept given her drugs regardless.
Michael wasn't an addict. But, the defense can and will argued that Michael shared some blame because if Murray didn't do what he wanted, Michael simply would had gone to someone else. So, it gives some people reasonable doubt not to blame Murray for everything, even though you may agree he acted like a selfish, idiot. The fact that Michael was willing to rig himself like a test subject every night doesn't help either.