Sometimes a Back-Alley Doctor, sometimes an otherwise respectable doctor, Dr. Feelgood serves as a catalyst for another character's dangerous or unethical prescription drug habit. They may have promised to "do no harm," but at the end of the day, they either are oblivious to the fact that the patient has a problem, or they just don't care.
They are getting quite rare nowadays as most medical regulating bodies are able to electronically track a physician's prescribing history and flag anything suspicious. In fact, there have been cases of doctors withholding nacotics from legitimate pain patients for fear of appearing like a Dr. Feelgood.
The Trope Namer is the Mötley Crüe song, in which the titular doctor does many things (including making cocaine for the Mexican mob.) Not to be confused with the Aretha Franklin song or the British pub rock band.
The doctor in Requiem for a Dream who continues to write Sara Goldfarb a prescription for diet pills, even when she complains of strange side effects and is clearly developing an addiction.
In The Cannonball Run, Dr. Nikolas van Helsing is the habit of injecting himself (and anyone else who asks for it) with the unspecified contents of a hypodermic he always carries, which causes him to get a blissful grin and then pass out.
House: Dr. Gregory House is his own Dr. Feelgood, what with the Vicodin addiction and all. However, due to the rules against doctors writing prescriptions for themselves, he usually has Wilson or one of his minions get the goods for him.
Referenced in an episode of Malcolm in the Middle, when a new neighbor asks Lois who her doctor is. Lois asks what the problem is, and the neighbor replies "back pain," and goes on to imply that she will say anything to get the pills she wants. Lois replies, "Sorry, my doctor's honest."
A New Tricks episode focusing on the death of a rock singer, had his former band mates point the detectives at 'Doc' who supplied them all with drugs back in the day. The guy turned out to be just a dealer rather than actual doctor.
A Victim of the Week on The Glades was one of these and the clinic he operated was a 'pill mill'. It turned out that the clinic was only one of a whole chain of pill mills operated by a corrupt medical company. Also the dead doctor was doing it so he could raise money for medical supplies to send to earthquake ravaged Haiti
Law & Order had a case once involving one of these. They had a little trouble coming up with a charge that would stick because the drugs he was prescribing and supplying weren't actually illegal.
Mötley Crüe's song is, of course, the Trope Namer, although it's never clear if the character so nicknamed is a doctor with profitable sidelines or a simple dealer with a memorable handle.
Rat-tailed Jimmy is a second hand hood/Deals out in Hollywood Got a '65 Chevy with primered flames/Traded for some powdered goods Jigsaw Jimmy, he's runnin' a gang/But, I hear he's doin' okay Got a cozy little job/Sells the Mexican mob/Packages of candycaine
"Mother's Little Helper," by The Rolling Stones, is about 1960s mothers needing to take prescription "uppers" to keep up with all their daily duties. It includes a warning about overdoses of prescription pills.
And though she's not really ill/There's a little yellow pill...
Doctor please, some more of these/Outside the door, she took four more.
The Beatles "Doctor Robert" from Revolver. "If you're down he'll pick you up/Take a drink from his special cup.../Well, well, well you're feeling fine/Well, well, well he'll make you"
An astoundingly honest and straight-forward one is the subject of 'I Buy The Drugs' by Electric Six.
Pink Floyd's "Comfortably Numb" has verses apparently sung by such a doctor (who's aiming to revive the KO'd protagonist to make him perform a show; the movie of the album shows it's not that glamorous):
Hello? Is there anybody in there? Just nod if you can hear me. Is there anyone home? Come on, Come on, Come on, now, I hear you're feeling down. Well, I can ease your pain Get you on your feet again.
Wendla, the female teenage protagonist in the original stage play of Spring Awakening, is killed by pills prescribed to her as an abortifacient. The doctor never tells her she's pregnant and insists they are for anemia.
The Venture Bros..: Dr. Venture visits a "Tijuana doctor" for a resupply of his pills. Initially the doctor balks at prescribing such a large amount of drugs. The doctor was insulted that Dr. Venture assumed he'd just grant a prescription because he was a Mexican doctor. Dr. Benjamin helped smooth the ruffles.
Dr. Potterswheel in Moral Orel gives Bloberta painkillers in response to her mutilating her lower region with a jackhammer, as he's turned on by this. He's also revealed to be a widower who also gave his wife painkillers as opposed to actually treating her, which may have resulted in her death.
Perhaps one of the best known cases is that of Dr. George Nichopoulos (also known as, Dr. Nick,) who prescribed Elvis Presley drugs from 1967 until his death in 1977. "Dr. Nick" gave Elvis his ultimately fatal supply.
Michael Jackson seems to have accessed pain killers through several of these, and a particularly unethical one, Conrad Murray, was found guilty of involuntary manslaughter and grievous negligence in his death by prescribing a surgical anesthetic as a sleep aid.
The Beatles song "Dr. Robert" was about the real-life New York City doctor Max Jacobson (despite the National Health reference) whose nickname was the Trope Namer. He got involved with JFK, giving him several controversial treatments. Some of these involved illegal drugs such as methamphetamines. Many of Kennedy's medical problems and treatments were only recently declassified
This was actually the modus operandi of infamous Serial Killer Dr. Harold Shipman, deliberately getting his patients addicted to prescription painkillers until he finally killed them by overdose. Much was made of the fact that his mother had apparently depended heavily on morphine for pain relief during the final months before she succumbed to cancer, various armchair psychologists speculating about the effect this might have had on her son at an impressionable age, but the fact that so many of his victims ended up leaving him large amounts of money suggests a more mundane explanation. The truth will remain a mystery for the ages as Shipman hanged himself in his prison cell without ever giving anyone a straight answer about his motives.