Weight-Loss Drugs: A Historical Review, Part 1

April 11, 2024


Katrina Bishop
Policy Analyst


ACHI Communications

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Americans have turned to a variety of drugs over the past century in the pursuit of weight loss. From late-19th-century thyroid extracts to modern-day medications, the landscape of weight-loss drugs has been marked by scientific breakthroughs, controversies, and regulatory changes. This post begins a two-part look at the history of weight-loss medications.

From Thyroid Extract to Rainbow Diet Pills

As early as the 1890s, thyroid extract was being used for weight reduction due to the belief that it could boost metabolism and promote weight loss in individuals with normal thyroid function. It was thought that thyroid extract would increase a person’s metabolic rate, leading to more calories burned and, consequently, weight loss. However, the use of thyroid extract for this purpose was not without risks, such as weakness and palpitations.

Dinitrophenol, also known as DNP, emerged as a popular over-the-counter treatment for obesity in the 1930s. DNP works by interfering with cells’ production of energy. Normally, cells use nutrients to make a substance called adenosine triphosphate (ATP), which provides energy for the body. DNP disrupts this process, causing the body to burn more energy to try to make up for the lost ATP. This can lead to a dangerous increase in body temperature, which can cause organ damage and, in severe cases, death. Other potential effects of DNP included breathing problems, a buildup of acid in the body, and heart problems.  As a result of growing reports of severe side effects, dinitrophenol was labeled as “extremely dangerous and not fit for human consumption” under the Federal Food, Drug, and Cosmetic Act of 1938.

In 1937, Benzedrine Sulfate, the brand name for amphetamine sulfate, was introduced to treat a variety of medical conditions, including narcolepsy and minor depression. During World War II, Benzedrine, supplied by the US military, surged in popularity among pilots and air crews as a way to overcome fatigue and boost morale. Further research showed that amphetamine also suppressed appetite, a discovery that energized the weight-loss industry. In 1941, Clark & Clark of Camden, NJ, was one of the first manufacturers of diet pills to combine amphetamine sulfate with other drugs to counteract amphetamine’s unwanted side effects. These diet pills were among the first mass-produced rainbow diet pills.

Rainbow diet pills, named for their bright and varied colors, are a combination of amphetamines, barbiturates, thyroid extract, diuretics, and laxatives. The combination of ingredients in rainbow diet pills led to a range of serious side effects. Amphetamines led to increased heart rate, elevated blood pressure, insomnia, and addiction. Barbiturates, used to counteract the stimulant effects of amphetamines, led to drowsiness, confusion, and addiction. The addition of thyroid extract, diuretics, and laxatives to the mix led to electrolyte imbalances, dehydration, and gastrointestinal issues.

Growing concern over the serious health risks associated with rainbow diet pills led the federal government to implement stricter regulations, including the Drug Abuse Control Amendments of 1965, which increased accountability for the use of amphetamines in medical practice, and the Comprehensive Drug abuse Prevention and Control Act of 1970, which established different schedules for certain drugs based on their medical value in relation to their abuse potential. 

The Bottom Line

While substances like thyroid extract, dinitrophenol, and amphetamines were initially embraced for their perceived effectiveness in combating obesity, their usage was soon overshadowed by serious health risks and regulatory restrictions. Novel research and development paved the way for a new generation of weight-loss drugs in the 21st century.

In our next post, we will explore developments in weight-loss drugs over the past few decades, including the rise of popular drugs such as Ozempic and Wegovy. See also our previous installments in this series, covering how the new weight-loss drugs work, what they mean for children with obesity, what they cost, and other key considerations.

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