There is a clear difference between opium and cocaine in the stories. Both Holmes and Watson disapprove of opium use; Watson also disapproves of cocaine, though Holmes uses it. Note that on almost every other occasion when the two have a difference of opinion, Holmes turns out to be right and Watson is exposed as too unimaginative and rigid a thinker. I think Doyle’s message is perfectly clear.
There is a clear difference between opium and cocaine in the stories. Both Holmes and Watson disapprove of opium use; Watson also disapproves of cocaine, though Holmes uses it. Note that on almost every other occasion when the two have a difference of opinion, Holmes turns out to be right and Watson is exposed as too unimaginative and rigid a thinker. I think Doyle’s message is perfectly clear.