“Orexigenic” describes substances that stimulate appetite and promote increased food intake. These can include drugs, hormones, or other biological compounds. Understanding orexigenic effects is important because they play a role in the body’s system for maintaining energy balance. This concept often contrasts with “anorexigenic,” which refers to signals that suppress hunger and reduce food consumption.
How the Body Regulates Hunger
The body regulates hunger through a complex system, primarily centered in the brain’s hypothalamus. Specialized nerve cells, known as orexigenic neurons, reside in this region and drive the sensation of hunger. These neurons release neuropeptides, such as neuropeptide Y (NPY) and agouti-related protein (AgRP), which act on brain circuits to increase appetite and encourage eating.
Beyond these brain-specific neuropeptides, several hormones also signal hunger to the brain. Ghrelin, often called the “hunger hormone,” is produced in the stomach when empty and directly stimulates orexigenic neurons. Another hormone is orexin, produced in the hypothalamus, which promotes wakefulness and stimulates food intake, especially in response to low energy states. The interplay between these hunger-promoting signals and appetite-suppressing, or “anorexigenic,” signals creates a delicate balance to regulate body weight and energy stores.
Common Orexigenic Compounds
Many substances and medications can induce an orexigenic effect by influencing the body’s natural hunger pathways.
Antidepressants, for example, can increase appetite and weight gain by affecting brain neurotransmitter systems that regulate mood and appetite. This may involve serotonin or norepinephrine pathways, altering hunger and satiety signals.
Some antipsychotic medications are known to stimulate appetite. They can influence receptors in the brain, including histamine and serotonin receptors, leading to increased food intake and weight gain. Similarly, certain antihistamines, used for allergies, can block histamine receptors in the brain, increasing appetite.
Cannabinoids, found in cannabis, are recognized for stimulating hunger, often called “the munchies.” These compounds interact with the endocannabinoid system, which regulates appetite, mood, and pain. Activating cannabinoid receptors in the brain can enhance the desire to eat. Steroid hormones, such as corticosteroids, can increase appetite and lead to weight gain by influencing metabolic processes and central appetite regulation.
Medical Uses of Appetite Stimulants
While increased appetite can be an unintended side effect, stimulating hunger is a desired therapeutic outcome in specific medical contexts. Individuals with severe appetite loss or involuntary muscle wasting, known as cachexia, can benefit from orexigenic substances. This is important for cancer patients, as chemotherapy and radiation often cause nausea and severe appetite loss, leading to weight loss and malnutrition.
Patients with advanced human immunodeficiency virus (HIV) or acquired immunodeficiency syndrome (AIDS) often experience cachexia; appetite stimulants can improve their nutritional status and quality of life. Similarly, individuals with anorexia nervosa, who have very low body weight due to restricted eating, may be prescribed these agents to encourage weight restoration. For those with cystic fibrosis, a genetic disorder affecting nutrient absorption and weight, appetite stimulants can support better caloric intake and growth. In these situations, the goal is to enhance nutritional intake, promote healthy weight gain, and support recovery.
Managing Unwanted Appetite Increases
Increased appetite, especially when leading to unintended weight gain, can be a challenging side effect of medications or a symptom of underlying dysregulation. Unwanted weight gain can contribute to health concerns, including metabolic issues and cardiovascular risks. Addressing this requires balancing the benefits of necessary medications with managing their effects on appetite.
For individuals experiencing an undesired increase in hunger, dietary adjustments are important. This involves focusing on nutrient-dense, lower-calorie foods, increasing fiber intake for satiety, and planning regular, balanced meals to avoid excessive hunger. Lifestyle changes, such as regular physical activity, can also help manage weight and improve metabolic health. Consult a healthcare professional if increased appetite becomes problematic; they can assess medication adjustments, alternative treatments, or dietary guidance.