Did Sherlock Holmes smoke opium in his pipe?

No, he did not. He smoked a shag tobacco kept in a Persian slipper on the mantel. He evidently did visit a opium den during his detective work, though whether he actually smoked any opium was not stated.
I don't believe so, although he did disguise himself as an opium taker in "The Man with the Twisted Lip".

He did, however, inject himself with cocaine on various occasions, took morphine, and smoked.

Sherlock Holmes was never an opium addict. Holmes was known to use a 7% solution of cocaine. He did this when there was no case to occupy his brain.

Upon reading one of the later books in the series, "The man with the twisted lip", I recall reading a conversation between Holmes and Watson, with Holmes introducing the matter in the form of '...I suppose Watson that you imagine that I have added opium-smoking to cocaine-injections and all the other little weaknesses on which you have favoured me with your medical views...' displaying perfectly the cause for question without a confirmed answer. I believe the thought of Sherlock Holmes and opium to be merely put together in regards to seek the clues of a case and nothing of recreational purpose.