Famously, the CIA was testing the hallucinogenic drug LSD in the 1950s and 60s, dosing hundreds of unsuspecting civilians and military personnel.
Japan, during WWII, had developed a form of methamphetamine that was issued to military personnel to stave off hunger and stay awake... under the brand name of Philopon (ヒロポン).
It was the war, and nobody was allowed to question anything.
Because of the era, nobody had really studied possible side-effects. It hits the brain and triggers waves of released dopamine and norepinephrine - and is highly addictive... but we know that now... and Japan kind of figured that out by the war's end.
It can also make the user hyper-sexual. Which may also explain the rash of violent sex crimes going on in Japan following WWII... on it's own soil..... returning military personnel and all that.
Created by a Dr. Muira for the Dainippon Pharmaceutical Company (nowadays it is Sumitomo Dainippon Pharma) and given out to the military starting in 1941, Philopon got its name from the Greek philo (love) and ponos (labor).
That's why the drug has a name that can't be properly pronounced by its Japanese population.
Factory workers helping keep the war machine rolling took Philopon to ward of hunger. Soldiers used it as a means to keep on soldiering when they got tired...
Let's not judge too harshly, the American soldiers got Benedrine (it allows the body to release adrenaline into the system)...
But... when the war was over, Japan had an incredible reserve of the stuff... and because it was addictive, many a Japanese soldier came back needing a fix... so it was sold to them... and sold to the populace... and it wasn't that expensive... which is good because most people in Japan were dirt poor, starving and out of work.
The next thing you know, there's a lot of people in Japan addicted to the stuff - upwards of around 1.5 million... but I suspect that number is just representative of how many people tried it at least once.
Police estimates in 1954 peg the number of addicts at around 550,000.
It took Japan until 1951 to ban production of the drug, but that just puts everything underground with more production than ever before.
Japan, via its police in 1954, began blaming the rash of illegal Philopon drug production on the Koreans--because it's never the Japanese fault.
Anyhow, the police began a major crackdown (ha-ha) on the drug peddlers and with 55,664 arrests in 1954... at its peak all the way down to 271 in 1958... which means they either weren't getting the job done or they were successful in halting illegal use.
This isn't to say that the Japanese weren't still taking a version of philopon after 1958, but it was no longer an epidemic.