Phentermine Vs. Topiramate: 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​.

Topiramate is the active ingredient in the brand-name medication Topamax^®. The information below is about brand name Topamax. 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.”

Topamax (topiramate) is an anticonvulsant medication used to treat seizures and prevent migraines by stabilizing electrical activity in the brain and reducing abnormal brain cell firing. Its FDA-approved indications include the treatment of epilepsy for partial onset or generalized tonic-clonic seizures and migraine prevention in adults and adolescents (12 and older). Topamax is available in tablet and sprinkle capsule forms, typically taken once or twice daily. Common side effects include dizziness, paresthesia, fatigue, weight loss, and trouble concentrating, and it carries a warning for increased risk of metabolic acidosis and kidney stones.

Sympathomimetic amine anorectic

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)

Topamax (topiramate) is indicated for:

• Epilepsy: initial monotherapy for the treatment of partial-onset or primary generalized tonic-clonic seizures in patients 2 years of age and older; adjunctive therapy for the treatment of partial-onset seizures, primary generalized tonic-clonic seizures, or seizures associated with Lennox-Gastaut syndrome in patients 2 years of age and older

• Preventive treatment of migraine in patients 12 years of age and older

• Typically taken orally once daily

• Comes in 37.5 mg tablets

• Typically taken orally with dosing based on indication and age group

• Comes in 25 mg, 50 mg, 100 mg, and 200 mg tablets and 15 mg and 25 mg sprinkle capsules

Adverse events have been reported in the following systems:

• Cardiovascular

• Central nervous system

• Gastrointestinal

• Allergic

• Endocrine

Epilepsy: Most common (≥10% more frequent than placebo or low-dose Topamax) adverse reactions in adult and pediatric patients were:

• Tingling

• Anorexia

• Weight loss

• Speech disorders/Related speech problems

• Fatigue

• Dizziness

• Sleepiness

• Nervousness

• Slowing down of physical and mental activities

• Abnormal vision

• Fever

Migraine: Most common (≥5% more frequent than placebo) adverse reactions in adult and pediatric patients were:

• Tingling

• Anorexia

• Weight loss

• Difficulty with memory

• Taste perversion

• Diarrhea

• Loss of sensation

• Nausea

• Abdominal pain

• Upper respiratory tract infection

• 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

• Drug interactions: contraceptives, lithium

• 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

• Acute myopia and secondary angle closure glaucoma

• Visual field defects

• Oligohidrosis and hyperthermia

• Metabolic acidosis

• Suicidal behavior and ideation

• Cognitive/Neuropsychiatric adverse reactions

• Fetal toxicity

• Withdrawal of AEDs

• Decrease in bone mineral density

• Negative effects on growth (height and weight)

• Serious skin reactions

• Hyperammonemia/Encephalopathy

• Kidney stones

• Hypothermia has been reported with and without hyperammonemia during topiramate treatment with concomitant valproic acid use

*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 Topamax^®. See the Full Prescribing Information for more complete information. Topiramate, the active ingredient in Topamax, may also be the active ingredient in other medications, and this information may not be accurate for all medications that include the active ingredient topiramate.