Phentermine Vs. Qsymia: Drug Comparison

Phentermine is the active ingredient in brand-name medications including Adipex-P^®. The information below is about brand name Adipex-P. According to the FDA, “Generic medicines use the same active ingredients as brand-name medicines and work the same way, so they have the same risks and benefits as the brand-name medicines.”

Adipex-P (phentermine hydrochloride) is a prescription medication used as a short-term adjunct to weight loss in patients with obesity. It works as an appetite suppressant by stimulating the central nervous system, which increases heart rate and blood pressure while reducing hunger. Adipex-P is typically prescribed alongside a reduced-calorie diet and exercise regimen to enhance weight loss efforts. Common side effects include increased heart rate, dry mouth, insomnia, and nervousness. It is important to note that Adipex-P is intended for short-term use due to the potential for dependence and other adverse effects​.

Qsymia^® (phentermine and topiramate) is a prescription medication used for chronic weight management in adults with obesity or overweight with at least one weight-related condition, such as hypertension, type 2 diabetes, or high cholesterol. It combines two active ingredients: phentermine, an appetite suppressant, and topiramate, which induces a feeling of fullness and reduces appetite. Qsymia is intended to be used alongside a reduced-calorie diet and increased physical activity. Common side effects include dry mouth, constipation, and tingling sensations in the hands and feet. It should be used with caution due to potential risks such as mood changes, increased heart rate, and birth defects if taken during pregnancy.

Sympathomimetic amine anorectic

Phentermine: sympathomimetic amine anorectic

Topiramate: anticonvulsant

Adipex-P (phentermine hydrochloride) is indicated:

• As a short-term adjunct (a few weeks) in a regimen of weight reduction based on exercise, behavioral modification and caloric restriction in the management of exogenous obesity for patients with an initial body mass index greater than or equal to 30 kg/m², or greater than or equal to 27 kg/m² in the presence of other risk factors (e.g., controlled hypertension, diabetes, hyperlipidemia)

Qsymia (phentermine and topiramate) is indicated:

• As an adjunct to a reduced-calorie diet and increased physical activity for chronic weight management in:

  • Adults with an initial body mass index (BMI) of:

    • 30 kg/m² or greater (obese) or

    • 27 kg/m² or greater (overweight) in the presence of at least one weight-related comorbidity such as hypertension, type 2 diabetes mellitus, or dyslipidemia

  • Pediatric patients aged 12 years and older with BMI in the 95th percentile or greater standardized for age and sex

• Typically taken orally once daily

• Comes in 37.5 mg tablets

• Typically taken orally once daily

• Comes in 3.75 mg/23 mg, 7.5 mg/46 mg, 11.25 mg/69 mg, and 15 mg/92 mg extended-release capsules

Adverse events have been reported in the following systems:

• Cardiovascular

• Central nervous system

• Gastrointestinal

• Allergic

• Endocrine

Most common adverse reactions in adults (incidence ≥5% and at least 1.5 times placebo) are:

• Tingling sensation

• Dizziness

• Altered taste

• Insomnia

• Constipation

• Dry mouth

Most common adverse reactions in pediatric patients aged 12 years and older (incidence ≥4% and greater than placebo) are:

• Depression

• Dizziness

• Joint pain

• Fever

• Influenza

• Ligament sprain

• History of cardiovascular disease (e.g., coronary artery disease, stroke, arrhythmias, congestive heart failure, uncontrolled hypertension)

• During or within 14 days following the administration of monoamine oxidase inhibitors

• Hyperthyroidism

• Glaucoma

• Agitated states

• History of drug abuse

• Pregnancy

• Nursing

• Known hypersensitivity, or idiosyncrasy to the sympathomimetic amines

• Drug interactions: Monoamine oxidase inhibitors, alcohol, insulin and oral hypoglycemics, adrenergic neuron blocking drugs

• Pregnancy

• Glaucoma

• Hyperthyroidism

• Taking or within 14 days of stopping monoamine oxidase inhibitors

• Known hypersensitivity to any component of Qsymia or idiosyncrasy to sympathomimetic amines

• Drug interactions: Oral contraceptives, central nervous system (CNS) depressants including alcohol, non-potassium sparing diuretics

• Coadministration with other drugs for weight loss is not recommended

• Rare cases of primary pulmonary hypertension have been reported

• Rare cases of serious regurgitant cardiac valvular disease have been reported

• Tolerance to the anorectic effect usually develops within a few weeks

• Adipex-P may impair the ability of the patient to engage in potentially hazardous activities such as operating machinery or driving a motor vehicle

• Risk of abuse and dependence

• Concomitant alcohol use may result in an adverse drug reaction

• Use caution in patients with even mild high blood pressure

• A reduction in dose of insulin or oral hypoglycemic medication may be required in some patients

• Breastfeeding: Discontinue drug or nursing taking into consideration importance of drug to mother

• Embryo-fetal toxicity: Can cause fetal harm

• Increase in heart rate

• Suicidal behavior and ideation

• Risk of ophthalmologic adverse reactions

• Mood and sleep disorders

• Cognitive impairment: May cause disturbances in attention or memory, or speech/language problems

• Slowing of linear growth

• Metabolic acidosis

• Decrease in renal function

• Serious skin reactions

• Breastfeeding: Breastfeeding not recommended

*This information is from the label for brand name Adipex-P^®. See the Full Prescribing Information for more complete information. Phentermine, the active ingredient in Adipex-P, may also be the active ingredient in other medications, and this information may not be accurate for all medications that include the active ingredient phentermine.

*This information is from the label for brand name Qsymia^®. See the Full Prescribing Information for more complete information.