Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
FASTIN vs TENUATE DOSPAN
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Sympathomimetic amine that promotes release of norepinephrine and dopamine from presynaptic nerve terminals in the hypothalamus, suppressing appetite.
Releases norepinephrine from nerve terminals in the lateral hypothalamic feeding center, reducing appetite.
Short-term adjunct in exogenous obesity,Off-label: Attention deficit hyperactivity disorder (ADHD)
Short-term adjunct in exogenous obesity,FDA-approved for obesity management
30 mg orally once daily in the morning, administered as a single dose.
25 mg orally three times a day, 1 hour before meals, or 75 mg extended-release orally once daily in the morning.
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.
The terminal elimination half-life is approximately 4-6 hours in adults with normal renal function, though clinical effects may last longer due to tissue distribution.
Hepatic metabolism via CYP3A4 and CYP2D6; active metabolite phendimetrazine (for some formulations).
Hepatic via CYP3A4 and other CYP enzymes
Primarily renal (approximately 70-80% unchanged) and biliary/fecal (20-30% as metabolites). Urinary excretion is p H-dependent; acidic urine increases elimination.
Renal excretion of unchanged drug and metabolites; approximately 85-90% of the dose is excreted in urine within 48 hours, with less than 5% in feces.
Approximately 40-50% bound to plasma proteins (albumin).
Approximately 20-30% bound to plasma proteins.
Approximately 3-5 L/kg. High Vd indicates extensive tissue distribution, including brain.
Approximately 5-10 L/kg, indicating extensive tissue distribution.
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.
Rapidly absorbed from the gastrointestinal tract; absolute oral bioavailability is about 10-20% due to extensive first-pass hepatic metabolism.
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.
Contraindicated in severe renal impairment (Cr Cl <30 m L/min). For moderate impairment (Cr Cl 30-59 m L/min), use with caution and consider dose reduction.
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.
Contraindicated in severe hepatic impairment. For Child-Pugh A or B, use with caution and consider reducing dose to 12.5 mg twice daily.
Not recommended for pediatric patients under 16 years of age due to lack of safety and efficacy data.
Not recommended for use in children under 12 years. For adolescents 12-17 years, same adult dosing may be used under strict supervision.
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.
Initiate at lower dose (12.5 mg twice daily) due to increased sensitivity and risk of adverse effects. Maximum dose 75 mg per day.
None.
None
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).
Pulmonary hypertension,Valvular heart disease,Seizures,Psychiatric disturbances,Tolerance and dependence,May impair ability to drive or operate machinery
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.
Advanced arteriosclerosis,Cardiovascular disease,Moderate to severe hypertension,Hyperthyroidism,Glaucoma,Agitated states,History of drug abuse,During or within 14 days of MAOI therapy
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.
No specific food interactions. However, avoid excessive caffeine intake as it may increase stimulant effects. Take with or without food; high-fat meals may delay absorption.
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.
FDA Pregnancy Category X: Teratogenic effects demonstrated in animal studies; contraindicated in pregnant women due to increased risk of fetal malformations, particularly in the first trimester. Potential for neonatal withdrawal symptoms (hyperexcitability, feeding disorders) with third trimester exposure.
Excreted in human milk; M/P ratio not established. Potential for adverse effects in nursing infants (irritability, poor feeding). Contraindicated during breastfeeding.
Excretion in human milk unknown; risk of serious adverse reactions in nursing infants (e.g., CNS stimulation, growth suppression). Use during breastfeeding contraindicated. M/P ratio not established.
Contraindicated in pregnancy; no dose adjustments recommended.
No dose adjustment possible; drug contraindicated entirely during pregnancy due to known teratogenicity. If pregnancy occurs, discontinue immediately and manage with alternative therapy.
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.
TENUATE DOSPAN (diethylpropion) is a schedule IV controlled substance used as an adjunct in obesity management. Avoid concurrent use with MAOIs due to hypertensive crisis risk. Monitor for tachyphylaxis and potential for abuse; limit use to short-term (up to 12 weeks). Contraindicated in patients with hyperthyroidism, glaucoma, or history of drug abuse.
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.
Take exactly as prescribed; do not increase dose or frequency.,Do not crush or chew the controlled-release tablet; swallow whole.,Report any chest pain, palpitations, or shortness of breath immediately.,Avoid alcohol and other CNS stimulants.,Use caution when driving or operating machinery until you know how this drug affects you.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about FASTIN vs TENUATE DOSPAN, answered by our medical review team.
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.. TENUATE DOSPAN is a Sympathomimetic anorectic that works by Releases norepinephrine from nerve terminals in the lateral hypothalamic feeding center, reducing appetite.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between FASTIN and TENUATE DOSPAN 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 FASTIN is: 30 mg orally once daily in the morning, administered as a single dose.. The standard adult dose of TENUATE DOSPAN is: 25 mg orally three times a day, 1 hour before meals, or 75 mg extended-release orally once daily in the morning.. 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 FASTIN and TENUATE DOSPAN 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. 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. TENUATE DOSPAN is classified as Category C. FDA Pregnancy Category X: Teratogenic effects demonstrated in animal studies; contraindicated in pregnant women due to increased risk of fetal malformations, particularly in the fi. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.