In reading the literature, it seems that a goodly number of upper-class people in Victorian England used opiates.
The famous surgeon (Sir William Osier) was a user of intravenous opium, and Sir Thomas de Quincey wrote about his drug experiences (“Confessions of an English Opim Eater”).
We most of these addicts able to function normally, despite using these drugs?
Which leads to my second question-was it fashionable (in literary circles) to be a drug user? Was it thought to stimulate creativity?
The Sherlock Holmes story The Man With the Twisted Lip (1891) involves an opium den, and does not present its users in a favourable light. Obviously it’s fiction, but perhaps it serves as an example of attitudes towards the drug at the time. Note that Conan Doyle was a physician.
opium smoking was never widespread among whites, certainly not in Europe or America (not sure about expats in Colonial India). Morphine use was a relatively widespread vice in the middle class, though less widespread than chronic alcoholism. Yes, they were able to function normally, and indeed they functioned much better than the chronic alcoholics. Some alcoholics were successfully transitioned to using morphine as the lesser evil - less destructive to health, less interfering with getting work done and cheaper given price structure back then.
If you are looking for stuff popular with the bohemians, that would be cocaine sniffing.
Apart from smoking the stuff, laudanum, which was tincture of opium, was widely used for a variety of medicinal purposes. Because it was so heavily prescribed, addiction was common. It was so widely available that recreational use probably occurred as well:
From Laudanum - Wikipedia
I think what you should be getting from the literature is a significance to the character from this particular flaw in their moral behavior. Opium and morphine are useful medicines – they stop coughs, a treat diarrhea, two very common problems in a pre-antibiotic world. Staunching diarrhea may just keep someone from dying, and not scarring one’s lungs is useful for longevity too. People were well aware that these things were additive, and they did care, about their loved ones and the behavior of “great” people. But there was always the undercurrent – if you succumb to addition, it is because you are weak. Socially, morally, genetically, and in some sense at the time, all three were synonyms, weak. The opiate or (Sherlock Holmes’s cocaine addition) were good, quick, cheap, commonly understood flaws you could just slip into a character to move the story along.
I believe that Paragoric (anhydrous morphine) is still available, but maybe not widely prescribed. I recall my folks rubbing it on my gums to ease tooth pain. This was in the 50’s.
Is it really any different than Laudnum?
you can add edgar allan poe to your list of fiends.
O. Henry’s short stories (ca. 1900) contain many references to middle class drug use-intravenous use was common then.
Couldn’t be much worse than heavy booze use.
Good book: Opium and the Romantic Imagination by Alethea Hayter.
You can’t say there’s a single attitude towards drug use in the Victorian era any more than today. My medically-based and beneficial use of laudanum (yes, perhaps my health requires it on almost a daily basis, but that’s medicine) is far, far, different from the vicious addiction of the coolie in his opium den.
In the Holmes stories for instance, a gentleman being found in an opium den would be evidence of abject degradation and failure, while Sherlock’s use of intravenous cocaine is more of a semi-minor character flaw.
Also, “Portrait of a Lady” (James, right?)
Sherlock preferred nose candy, anyway.
It’s obviously the better choice. I mean, it’s stimulating! What could possibly sniff go twitch wrong?
Louisa May Alcott apparently preferred 420.
Technically, I think it was arm candy for him.
Not quite ready to click that link from work. 
what’s 420? Is it pot?
Yes, 420 is pot, and Louisa and her father both smoked it, to the best of our ability to tell. It is worth noting that it wasn’t illegal (or particularly noteworthy - other than the stigma of a woman smoking in the first place) to do so.