This is one of those "debunked" things. Fake news is what mainstream would call it.

https://web.archive.org/web/20220228193458/https://truth11.com/2009/12/01/nazi-connections-to-flouride-in-americas-drinking-water/

The story begins in 1924, when Interessen Gemeinschaft Farben (I.G. Farben), a German chemical manufacturing company, began receiving loans from American bankers, gradually leading to the creation of the huge I.G. Farben cartel. In 1928 Henry Ford and American Standard Oil Company (The Rockefellers) merged their assets with I.G. Farben, and by the early thirties, there were more than a hundred American corporations which had subsidiaries and co-operative understandings in Germany. The I.G. Farben assets in America were controlled by a holding Company, American I.G. Farben, which listed on it’s board of directors: Edsel Ford, President of the Ford Motor Company, Chas. E. Mitchell, President of Rockerfeller’s National City Bank of New York, Walter Teagle, President of Standard Oil New York, Paul Warburg, Chairman of the federal reserve and brother of Max Warburg, financier of Germany’s War effort, Herman Metz, a director of the Bank of Manhattan, controlled by the Warburgs, and a number of other members, three of which were tried and convicted as German war criminals for their crimes against humanity. In 1939 under the Alted agreement, the American Aluminum Company (ALCOA), then the worlds largest producer of sodium fluoride, and the Dow Chemical Company transferred its technology to Germany. Colgate, Kellogg, Dupont and many other companies eventually signed cartel agreements with I.G. Farben, creating a powerful lobby group accurately dubbed “the fluoride mafia”(Stephen 1995).

Arent all these people, technically criminals to the american public? Anyway.

In 1987, Ian E. Stephens authored a self-published booklet, an extract of which was published in the Australian New Age publication Nexus in 1995. In it he claimed he was told by "Charles Elliot Perkins" that: "Repeated doses of infinitesimal amounts of fluoride will in time reduce an individual's power to resist domination by slowly poisoning and narcotising a certain area of the brain and will thus make him submissive to the will of those who wish to govern him ... Both the Germans and the Russians added sodium fluoride to the drinking water of prisoners of war to make them stupid and docile." These statements have been dismissed by reputable Holocaust historians as untrue, but they are regularly repeated to the present day in conspiracy publications and websites.[94]

Plenty of sources debunking it. But I want to point out something here.

https://cen.acs.org/articles/94/i41/Nazi-origins-deadly-nerve-gases.html

As it happens so often in science research, nerve agents were discovered accidentally. Gerhard Schrader, a 33-year-old German chemist at the IG Farben chemical conglomerate, had been tasked with developing new insecticides. The goal, mandated by Third Reich strategists, was to reduce Germany’s reliance on food imported from abroad. To do so, the country needed to prevent insect pests from depleting its food supply.

After several setbacks—Schrader had failed to make viable fluorine- and sulfur-based pesticides—the chemist began to experiment with molecules that combined phosphorus and cyanide.

https://www.psychiatrictimes.com/view/world-wars-modern-neuropsychopharmacology

In the years after World War II, there were no effective medicines for schizophrenia, bipolar disorder, or major depression. There were not even names for such things. The word antipsychotic was first used at a medical meeting in 1956, antidepressant was coined in 1952, and tranquilizer in 1953, but their acceptance was slow. Yet within the next 2 decades, all these types of medicines were developed. Most of drug discoveries occurred inadvertently, often with a chance observation by a physician or scientist who was looking for something else.

Many of the key figures in modern psychopharmacology were caught up in World War II in one way or another.1 Some like Henri Laborit, MD, who later initiated the use of chlorpromazine for psychoses, and John Cade, MD, who made the modern rediscovery of lithium for bipolar disorder, were military physicians. In both cases, one can see the influence of wartime experiences on their later work. Laborit was aboard a French destroyer struck by torpedoes during the evacuation of Dunkirk and was awarded a Military Cross for his actions during its sinking. After the development of chlorpromazine, he quickly suggested that it might be useful in managing stress in wounded soldiers on the battlefield (which proved to be an unsuccessful, even disastrous, endeavor). Cade volunteered for service in the Australian Army; he served in Singapore until he was captured and spent several years as a prisoner of the Japanese. While caring for fellow prisoners of war, he noticed their fluctuating levels of mental clarity, and wondered if this might be related to changing amounts of circulating substances, foreshadowing his later studies that led to lithium.

https://pubmed.ncbi.nlm.nih.gov/19125905/

The pharmaceutical industry and the German National Socialist Regime: I.G. Farben and pharmacological research

Before the National Socialist party came to power, the German pharmaceutical industry constituted an international reference as far as the development of new medicines was concerned, having been responsible for synthetic analgesics (phenacetin, phenazones, acetylsalicylic acid), arsphenamine, barbiturates and sulfonamides. The year 1925 saw the founding of I.G. Farben (Interessen-Gemeinschaft Farbenindustrie AG), a conglomerate of companies that would monopolize the country's chemical production and come to own all its major pharmaceutical industries. During the World War II, I.G. Farben participated in numerous operations associated with the criminal activities of the Nazi executive, including the use of slave labour in plants built close to concentration camps, such as that at Auschwitz. With regard to medical and pharmacological research projects, I.G. Farben became involved in experimental programmes using patients from the Nazi regime's euthanasia programmes and healthy subjects recruited without their consent from concentration camps, on whom various pharmacological substances were tested, including sulfamide and arsenical derivatives and other preparations whose composition is not precisely known (B-1012, B-1034, 3382 or Rutenol, 3582 or Acridine), generally in relation to the treatment of infectious diseases, such as typhus, erysipelas, scarlet fever or paratyphoid diarrhoea. Furthermore, I.G. Farben played a decisive role in the German army's chemical warfare programme, contributing to the development of the first two neurotoxic substances, later known as 'nerve agents', tabun and sarin. Some of these activities came to light as a result of the one the famous Nuremberg Trials in 1947, which saw 24 executives and scientists from I.G. Farben brought to justice for, among other offences, the use of slave labour in the concentration camps and forced experimentation with drugs on prisoners.

While there is no proof, it certainly seems plausible, hell even likely considering everything this one guy had his hands in.