Long term famous functional drug addicts?

nitrous oxide is one of the most addicitve things i have ever done

Paul Erdös was the most prolific mathematician ever, and a heavy user of amphetamines for more than 20 years.

Edgar Allan Poe (alcohol and opium), apparently the extent to which he was an opium addict is now disputed - when I was a child it was a given that Poe was a junkie.
Lucy Maud Montgomery (goofballs)

Lemmy…

From the same era, Thomas de Quincey (“Confessions of an English Opium Eater”)

Heck, we can throw in nicotine and have thousands of examples of functional addicts.

Ray Charles.

Aye, of course we could. Churchill was a high-functioning alcoholic though, and that meets the criteria of the OP. By modern standards FDR probably was too, but Churchill was a massive alkie by any standard.

I’ve read that he exaggerated that in order to maintain a certain image, and often appeared at parties with a glass of whiskey which was really greatly watered down.

Here’s a (probably biased) website which discusses it.

I don’t think he ever drank massive amounts of spirits, to be fair. Pol Roger as a breakfast* tipple though…

*Not that he was much of an early riser

Erdős, actually. Although he did take amphetamines daily, he vehemently denied accusations that he was addicted. A colleague bet him $500 that he couldn’t stop taking the drug for a month; Erdős easily won the bet, but complained that his abstinence had set back the progress of mathematics by a month: “Before, when I looked at a piece of blank paper my mind was filled with ideas. Now all I see is a blank piece of paper.” Erdős resumed taking the drug after winning the bet.

It has no addiction syndrome at all. Being inclined to do something repeatedly because you find it fun doesn’t count as an addiction. Anyway, Leary’s regular nitrous use was as a palliative anaesthetic at the end of his life, with the aim of reducing his dependence on morphine.

Many powerful people have personal physicians who will supply them with “legal” drugs, via prescription.
Take Adolf Hitler-his personal doctor (Dr. Theo Morell) regularly gave injections to Hitler-probably composed of multiple drugs.
J.F. Kennedy had his own doctor (Dr. Max Jacobs) who also supplied him with injections (of a multi-drug) cocktail.
And (of course) the late Michael Jackson-his doctor kept him doped up…

Christopher Hitchens (alcohol, not to mention tobacco). Granted, he died pretty young (62), but he had a functional career as a writer and speker right up until the end.

Can we mention famous fictional characters too? Sherlock Holmes.

Your friend has double vision.

Sigmund Freud was a cocaine addict. After surgery (successful) for oral cancer, he went back to smoking cigars.

Somebody’s feeling Moody today.

Hermann Göring was addicted to opiates from 1923 until shortly before his death in 1945.

Nick Cave. I’ve heard he quit heroin at some point but am not sure when that was or if he’s still clean. Anyhow, he was definitely a long term user.