The (brief) History of Steroids by Jamie Lewis aka Plague of Strength. Taken from an Instagram post of his and way cool
1935- Testosterone is isolated in Amsterdam and synthesized in Germany later that year.
1954- Russian athletes are given large doses of testosterone in preparation for the Olympics.
1955- Dianabol is born. This oral steroid immediately becomes massively popular in the Soviet Union.
1958- Dr. John Ziegler begins promoting dianabol use for weightlifters and bodybuilders in the United States based on results obtained from Soviet experiments with the drug.
1966- Natty bro Chet Yorton beats Arnold for the Mr U. Says steroids are getting too prevalent and retires.
1975- Powerlifter Tony Fitton undermines a UK steroid study and uses the dianabol he obtained in the process to set up a steroid empire. Within a few years, Tony Fitton is the biggest steroid dealer in the world.
1977- first tested bodybuilding federation is founded by Chet Yorton.
In short, virtually no one was on steroids before 1954.
Before 1965, the people using steroids were almost exclusively Olympic weightlifters. Anyone who trained with the York guys after 1960 might have been gassed up (which includes Bob Peoples and Paul Anderson), and Muscle Beach definitely had them by the mid-1960s, but they weren't predominantly used until the mid-1970s, when they became widely available thanks to Tony Fitton (who must've saved a lot of money by somehow never using them himself, by the looks of him).
After 1975, steroids were added to the amphetamine use that was already completely ubiquitous in pro sports, from baseball to wrestling and everything in between (even housewives were filled with the shit, and it seems the entire Western world had a meth problem for a couple of decades in the mid-20th century).