Amphetamines are central nervous system stimulants. Their primary medical applications include managing attention-deficit/hyperactivity disorder (ADHD) and the sleep disorder narcolepsy, where they help improve focus and promote wakefulness. In some specific cases, such as with lisdexamfetamine, they are approved for treating binge-eating disorder. Beyond these prescribed uses, amphetamines exert significant physiological effects, one of which is weight loss resulting from complex interactions within the brain and nervous system.
The Mechanism of Weight Loss
The process by which amphetamines induce weight loss is twofold, involving both appetite suppression and an increase in metabolic activity. The brain’s hypothalamus, a region that helps regulate hunger and feelings of fullness, is a primary site of action. Amphetamines increase the release and slow the reuptake of key neurotransmitters, dopamine and norepinephrine, in this area. This elevation in neurochemical signaling dampens the body’s natural hunger cues, leading to a reduced desire to eat.
These drugs also directly stimulate the sympathetic nervous system, the network responsible for the “fight-or-flight” response. This activation prepares the body for activity, resulting in changes that increase energy consumption, such as an accelerated heart rate and higher core body temperature (thermogenesis). This stimulation also promotes lipolysis, the breakdown of stored fats into fatty acids for energy. The combined effect of eating less and burning more calories creates the energy deficit that drives weight loss.
Medical Prescription for Weight Management
The use of amphetamines for weight management has a long history, beginning in the 1930s and 1940s when their appetite-suppressing effects were first recognized. Drugs like Benzedrine became popular as “diet pills,” and for several decades, they were a common prescription for those seeking to lose weight. This era also saw the emergence of “rainbow diet pills,” dangerous combinations of amphetamines and other substances.
Today, the medical approach is far more cautious and regulated. True amphetamines, such as those for ADHD like Adderall, are rarely prescribed off-label for weight management due to their health risks and high potential for misuse. Instead, professionals may turn to amphetamine-like substances with a different chemical structure and risk profile. Phentermine is the most common example, a drug that mimics some amphetamine effects but has a lower potential for dependence.
The prescription of these medications is governed by strict guidelines. Drugs like phentermine are approved only for short-term use, often for just a few weeks. They are reserved for patients with significant obesity, defined by a body mass index (BMI) of 30 or higher, or a BMI of 27 or higher if the patient also has weight-related health conditions. These drugs are not a standalone solution but a component of a comprehensive plan that includes a reduced-calorie diet and physical activity.
Health Risks and Side Effects
The use of amphetamines for weight loss carries substantial health risks, impacting the cardiovascular system. Users frequently experience an increased heart rate, palpitations, and elevated blood pressure. Over time, this added strain on the heart and blood vessels can increase the long-term risk of more severe events, including heart attack and stroke, especially when used at high doses or for extended periods.
Beyond the physical effects, there are significant psychological and neurological consequences. Common side effects include insomnia, anxiety, restlessness, and irritability. In some individuals, amphetamine use can escalate to more severe mental health issues, such as paranoia or a state of psychosis characterized by a disconnection from reality. These effects stem from the drug’s influence on brain chemistry.
One of the most concerning aspects of amphetamine use is the high potential for tolerance, dependence, and addiction. With continued use, the body adapts to the drug, leading to tolerance, where higher doses are needed to achieve the same effects. This can lead to dependence, a state where the body relies on the drug to function normally. Amphetamines are Schedule II controlled substances due to their high potential for misuse and substance use disorder.
Consequences of Discontinuation
When a person stops taking amphetamines after a period of use for weight loss, they often face a rapid rebound in weight gain. The drug’s appetite-suppressing and metabolism-boosting effects are gone, and the body’s natural hunger signals return, often with greater intensity. Because the weight loss was achieved through pharmacological intervention rather than sustainable lifestyle changes, many individuals regain the lost weight and sometimes more.
In addition to weight regain, stopping the medication can trigger a withdrawal syndrome. This condition is characterized by distressing physical and psychological symptoms like extreme fatigue, depression, and a sharp increase in appetite. The combination of rebound weight gain and a difficult withdrawal creates a challenging cycle, reinforcing a psychological reliance on the substance as a solution to both weight management and the negative feelings associated with stopping it.