Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
PHENDIMETRAZINE TARTRATE vs FASTIN
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Phendimetrazine is a sympathomimetic amine that acts as an appetite suppressant by stimulating the hypothalamus to release norepinephrine, leading to decreased food intake and increased energy expenditure. It is a prodrug that is metabolized to phenmetrazine, which is a potent central nervous system stimulant with amphetamine-like effects.
Sympathomimetic amine that promotes release of norepinephrine and dopamine from presynaptic nerve terminals in the hypothalamus, suppressing appetite.
Management of exogenous obesity as a short-term adjunct (a few weeks) in a regimen of weight reduction based on caloric restriction,Off-label: treatment of obesity with comorbid conditions where weight loss is beneficial
Short-term adjunct in exogenous obesity,Off-label: Attention deficit hyperactivity disorder (ADHD)
Oral: 35 mg twice daily or three times daily, 1 hour before meals; extended-release: 105 mg once daily in the morning.
30 mg orally once daily in the morning, administered as a single dose.
Terminal half-life 3-4 hours; clinical context: requires multiple daily dosing
Terminal elimination half-life is approximately 16-20 hours for the immediate-release formulation. With sustained-release forms, effective half-life may extend to 24-34 hours due to prolonged absorption. Clinical context: time to reach steady state is about 3-5 days.
Primarily metabolized in the liver via N-demethylation to its active metabolite, phenmetrazine. Other metabolites include phendimetrazine N-oxide and norphenmetrazine. CYP450 enzymes are involved, though specific isoforms not well characterized.
Hepatic metabolism via CYP3A4 and CYP2D6; active metabolite phendimetrazine (for some formulations).
Primarily renal (≥70% unchanged) with minor biliary/fecal elimination (<10%)
Primarily renal (approximately 70-80% unchanged) and biliary/fecal (20-30% as metabolites). Urinary excretion is p H-dependent; acidic urine increases elimination.
10-15% bound to albumin
Approximately 40-50% bound to plasma proteins (albumin).
2-3 L/kg; indicates extensive tissue distribution
Approximately 3-5 L/kg. High Vd indicates extensive tissue distribution, including brain.
Oral: approximately 80-90%
Oral immediate-release: ~90% (high first-pass metabolism; absolute bioavailability is lower, but systemic exposure is adequate). Oral sustained-release: similar extent but with prolonged absorption.
Contraindicated in severe renal impairment (GFR < 30 m L/min). No specific dose adjustments for mild-moderate impairment; use with caution.
Contraindicated in severe renal impairment (e GFR <30 m L/min/1.73 m²). For moderate impairment (e GFR 30-59 m L/min/1.73 m²), reduce dose to 15 mg once daily.
Not recommended in Child-Pugh class B or C. Use with caution in mild impairment.
Contraindicated in Child-Pugh class C cirrhosis. In Child-Pugh class A or B, initiate at 15 mg once daily and titrate cautiously to maximum 30 mg once daily.
Not recommended for children under 12 years; safety and efficacy not established.
Not recommended for pediatric patients under 16 years of age due to lack of safety and efficacy data.
Start at lower end of dosing range; monitor for increased sensitivity and cardiovascular effects.
Initiating at 15 mg once daily is recommended due to increased sensitivity and potential for central nervous system adverse effects; maximum dose 30 mg once daily.
Phendimetrazine is not approved for use in patients with a history of drug abuse or dependence. It has a high potential for abuse and may lead to dependence. Use caution in patients with cardiovascular disease or hypertension.
None.
Increased risk of pulmonary hypertension and valvular heart disease; monitor for dyspnea, chest pain, or edema. Tolerance may develop; discontinue if tolerance occurs. May impair ability to perform hazardous tasks. Use with caution in patients with hypertension, diabetes, or glaucoma. Do not use with MAOIs or within 14 days of discontinuation.
Cardiovascular events (hypertension, tachycardia, stroke), psychiatric adverse effects (psychosis, dependence), primary pulmonary hypertension, valvular heart disease, tolerance, withdrawal symptoms, glaucoma, hyperthyroidism, seizure disorder, diabetes (dose adjustment required), elderly patients (higher sensitivity).
Hypersensitivity to phendimetrazine or any component of the formulation, advanced arteriosclerosis, symptomatic cardiovascular disease, moderate to severe hypertension, hyperthyroidism, glaucoma, agitated states, history of drug abuse, during or within 14 days of MAOI therapy
Cardiovascular disease (e.g., coronary artery disease, arrhythmias, hypertension), hyperthyroidism, glaucoma, agitated states, history of drug abuse, MAOIs (concurrent or within 14 days), hypersensitivity to sympathomimetics.
Avoid alcohol and excessive caffeine (coffee, tea, energy drinks) as they may increase CNS stimulation and risk of side effects. Take with or without food; high-fat meals may delay absorption of extended-release formulations. Maintain a calorie-reduced diet as part of a comprehensive weight loss plan.
Avoid excessive caffeine intake (e.g., coffee, tea, cola, energy drinks) as it may potentiate CNS and cardiovascular effects. Grapefruit juice may alter drug metabolism; avoid concurrent consumption. Maintain a balanced, reduced-calorie diet as part of the weight loss plan. Alcohol should be avoided due to potential additive CNS effects.
First trimester: Limited data; potential for increased risk of oral clefts. Second/third trimester: Anorexiant effects may cause fetal growth restriction; avoid use due to maternal hypertension risk.
FDA Pregnancy Category X. First trimester: Increased risk of oral clefts and cardiac malformations with amphetamine use. Second and third trimesters: Risk of premature delivery, low birth weight, and neonatal withdrawal syndrome. Avoid use in pregnancy.
Excreted in breast milk; M/P ratio unknown. Contraindicated in breastfeeding due to potential CNS stimulation and cardiovascular effects in infant.
Excreted in human milk; M/P ratio not established. Potential for adverse effects in nursing infants (irritability, poor feeding). Contraindicated during breastfeeding.
Contraindicated in pregnancy; no dose adjustments recommended. Avoid use due to risks of hypertension and potential teratogenicity.
Contraindicated in pregnancy; no dose adjustments recommended.
Phendimetrazine tartrate is a schedule III controlled substance with high abuse potential. It is approved only for short-term (up to 12 weeks) monotherapy for exogenous obesity. Contraindicated in patients with glaucoma, hyperthyroidism, agitated states, history of drug abuse, or cardiovascular disease. Taper dose to avoid withdrawal. Monitor blood pressure and heart rate; may cause pulmonary hypertension. Avoid use with MAOIs (risk of hypertensive crisis) and within 14 days of discontinuation.
Fastin (phentermine) is a sympathomimetic amine indicated for short-term (up to 12 weeks) monotherapy for obesity. It should be used in conjunction with a reduced-calorie diet and exercise. Avoid co-administration with MAOIs or within 14 days of MAOI use due to hypertensive crisis risk. Use with caution in patients with hypertension, diabetes, or history of drug abuse. Monitor blood pressure and heart rate regularly. Tachyphylaxis may develop; discontinue if tolerance occurs. Do not use in patients with advanced arteriosclerosis, hyperthyroidism, glaucoma, or agitated states.
Take exactly as prescribed; do not increase dose or duration.,Take last dose of the day 4-6 hours before bedtime to prevent insomnia.,Do not crush or chew extended-release tablets; swallow whole.,Avoid driving or operating heavy machinery until you know how this medication affects you.,Report chest pain, shortness of breath, fainting, or leg swelling immediately.,Do not stop abruptly; follow your doctor's tapering plan.,Store securely; keep out of reach of others as this medication can be habit-forming.,Do not take with alcohol or other CNS stimulants.,Use with caution if you have high blood pressure, diabetes, or a history of depression.
Take Fastin exactly as prescribed, usually once daily in the morning to avoid insomnia.,Do not crush or chew the extended-release capsule; swallow whole.,Avoid taking late in the day to prevent difficulty sleeping.,Report any chest pain, palpitations, shortness of breath, or dizziness immediately.,Do not increase dose or take more frequently than prescribed; risk of dependence and side effects.,Fastin is for short-term use only (up to 12 weeks) and should be combined with a reduced-calorie diet and exercise.,Do not use if you have taken an MAO inhibitor in the last 14 days.,Avoid alcohol and other CNS stimulants (e.g., caffeine in large amounts) as they may increase side effects.,Do not stop abruptly; follow your doctor's instructions for tapering off.,Keep out of reach of children; misuse can cause severe cardiac toxicity.
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about PHENDIMETRAZINE TARTRATE vs FASTIN, answered by our medical review team.
PHENDIMETRAZINE TARTRATE is a Anorectic (Sympathomimetic) that works by Phendimetrazine is a sympathomimetic amine that acts as an appetite suppressant by stimulating the hypothalamus to release norepinephrine, leading to decreased food intake and increased energy expenditure. It is a prodrug that is metabolized to phenmetrazine, which is a potent central nervous system stimulant with amphetamine-like effects.. FASTIN is a Sympathomimetic Anorectic that works by Sympathomimetic amine that promotes release of norepinephrine and dopamine from presynaptic nerve terminals in the hypothalamus, suppressing appetite.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between PHENDIMETRAZINE TARTRATE and FASTIN depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of PHENDIMETRAZINE TARTRATE is: Oral: 35 mg twice daily or three times daily, 1 hour before meals; extended-release: 105 mg once daily in the morning.. The standard adult dose of FASTIN is: 30 mg orally once daily in the morning, administered as a single dose.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between PHENDIMETRAZINE TARTRATE and FASTIN in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. PHENDIMETRAZINE TARTRATE is classified as Category C. First trimester: Limited data; potential for increased risk of oral clefts. Second/third trimester: Anorexiant effects may cause fetal growth restriction; avoid use due to maternal. FASTIN is classified as Category C. FDA Pregnancy Category X. First trimester: Increased risk of oral clefts and cardiac malformations with amphetamine use. Second and third trimesters: Risk of premature delivery, lo. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.