Phentermine is a prescription medication used for short-term weight management, typically as an addition to a comprehensive plan involving reduced calories and increased physical activity. Eligibility is determined by a healthcare provider who assesses a patient’s medical history and current health status. The criteria for starting this treatment are strictly regulated, primarily focusing on the patient’s Body Mass Index (BMI), a screening tool calculated using weight and height to classify weight status. Understanding the specific BMI thresholds and associated health factors is necessary to determine if a person qualifies for a phentermine prescription.
Standard BMI Criteria for Prescription
The primary factor determining eligibility for phentermine is a patient’s Body Mass Index. The first criterion for a prescription is a BMI of 30 kilograms per meter squared (kg/m²) or greater, which corresponds to the clinical classification of obesity. This threshold allows the medication to be considered without the requirement of other specific health conditions.
The second threshold is a BMI of 27 kg/m² or greater, categorized as overweight. A person in this range is only eligible for phentermine if they also have at least one weight-related health condition, known as a co-morbidity. This combination indicates that the weight is contributing to measurable health risks, justifying the use of an appetite suppressant. The medication is intended for short-term use, traditionally a few weeks, to support the start of a weight loss journey.
Essential Health Conditions for Consideration
The BMI threshold of 27 kg/m² requires the presence of weight-related co-morbidities, which act as qualifying health conditions. These conditions demonstrate that the patient’s excess weight is increasing their risk for severe health problems.
Qualifying Co-morbidities
Qualifying co-morbidities include dyslipidemia (an abnormal level of fats like cholesterol in the blood) and Type 2 diabetes. Controlled high blood pressure, or hypertension, is also a condition that can qualify a patient with a BMI over 27 kg/m² for treatment.
Absolute Contraindications
The decision to prescribe phentermine depends on the drug’s potential interaction with the cardiovascular system, given its stimulant properties. Certain pre-existing conditions act as absolute contraindications, preventing the prescription regardless of BMI.
These disqualifiers include a history of cardiovascular disease, such as coronary artery disease, stroke, or congestive heart failure. Uncontrolled hypertension is also a contraindication, as the medication can further increase blood pressure and heart rate.
Due to the drug’s stimulating effect on the central nervous system, other conditions like hyperthyroidism or glaucoma are also contraindications. Hyperthyroidism already causes symptoms such as an increased heart rate, which phentermine could exacerbate. Furthermore, a history of drug abuse is a disqualifying factor because phentermine is a controlled substance with a potential for misuse.
Phentermine’s Mechanism of Action
Phentermine is chemically classified as a sympathomimetic amine, a type of stimulant that operates within the central nervous system. The drug’s primary function is to suppress appetite by affecting the levels of certain neurotransmitters in the brain. Specifically, phentermine promotes the release of norepinephrine and, to a lesser extent, dopamine from nerve endings in the hypothalamus.
The elevated presence of these neurotransmitters stimulates the sympathetic nervous system, mimicking the body’s “fight-or-flight” response. This stimulation reduces hunger signals, causing a decrease in food intake, which is the main driver of the weight loss effect.
Phentermine also appears to increase energy expenditure, which modestly boosts the body’s basal metabolic rate. By acting as an anorectic agent, the drug helps create the caloric deficit necessary for weight loss. This pharmacological action is intended only to support, not replace, sustained changes in diet and exercise.