I was laughing my ass off to this movie simple because I have phases of bad OCD and I could just relate so well that I thought it was really funny. It was comforting.

"Also, he was a pill popper in his later years."
This is what people in the mental health system call "self medicating". Many people in Hughes' time (and now but way more prior to the 70's and 80's) just didn't get help because they were often frightened of psychiatry of the times or because they didn't recognize that they had an illness. Some people were ashamed to admit that there was something wrong and went about trying to hide it. Because Hughes had money and power, he was able to isolate himself and thereby hide his illness from most people which exacerbated his symptoms. I'm sure many of his friends just didn't know what to do and probably catered to him.
I watched this movie with my boyfriend (who has OCD) thinking he'd relate or empathize with him but the scenes where he's repeating things and stuff with the closed off rooms etc., I heard snickering and turned around to see him chuckling to himself muttering
"I don't get it."
Guysgo figure.
GG's-Sophia: ". . .my dear husband Sal, may he rest in peace until
I
get there. . ."

OCD, Syph his sheltered childhood and his parents dying
He also suffered a bit of a head injury while making the movie Hell's Angels, which damaged the part of his brain which dealt with correcting errors etc. This probably made him a compulsive double-checker.
And he suffered several other injuries later in his life, several plane crashes etc. Poor guy can only imagine. The OCD must've been horrible, turning him into a complete recluse. It's amazing he was able to keep control over his business empire for so long.

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It wasn't proven that he had syphilis. A biographer(s) suggested that his due to his mental decline. Hitler was also suggested as may having suffered from it. Howard Hughes could have easily have afforded treatment. I'm sure he was regularly checked.
Medications taken following his near fatal airplane crash worsened his state of mental health.

It was more than just OCD. Hughes suffered from syphillis which probably triggered many of his mental health problems and paranoia. The numerous accidents and head injuries probably didn't help either. Also, he was a pill popper in his later years.