Is this usage of by itself grammatical? I know it's OK in the following sentences:
Will the dog be safe left in the car by itself? The door seemed to open all by itself. The computer shuts off by itself if you don't use it. The house stood by itself at the end of the street.
But in all these cases we've got a subject doing something by itself whereas in our sentence by itself refers to it which is not a subject but a direct object. Shouldn't it be rephrased: It cannot be drunk by itself or It cannot be being drunk by itself?