Ionamin, Fastin, Zantryl, Adipex-P, Obe-Nix-30
Classifications: anorexiant;
Therapeutic: appetite suppressant

Prototype: Diethylpropion
Pregnancy Category: C
Controlled Substance: Schedule IV


8 mg, 30 mg, 37.5 mg tablets; 15 mg, 18.75 mg, 30 mg, 37.5 mg capsules


Sympathetic amine with pharmacological similarity to amphetamine. Actions include CNS stimulation and blood pressure elevation.

Therapeutic Effect

Appetite suppression or metabolic effects along with diet adjustment result in weight loss in obese individuals.


Short-term (8–12 wk) adjunct for weight loss.


History of hypertension, moderate-to-severe hypertension, advanced arteriosclerosis, cardiovascular disease; hyperthyroidism; known hypersensitivity to sympathetic amines; agitated states; psychosis; schizophrenia; history of drug abuse; during or within 14 d of administration of MAO inhibitor; concurrent administration of selective serotonin reuptake inhibitors (SSRIs); valvular heart disease; glaucoma; pregnancy (category C), lactation, or children <16 y.

Cautious Use

Mild hypertension, diabetes mellitus.

Route & Dosage

Adult: PO 8 mg t.i.d. 30 min before meals or 15–37.5 mg q.d. before breakfast or 10–14 h before retiring


  • Ensure that at least 14 d have elapsed between the first dose of phentermine and the last dose of an MAO inhibitor.
  • Give 30 min before meals.
  • Do not administer if an SSRI is currently prescribed.
  • Store in a tight container.

Adverse Effects (≥1%)

Body as a Whole: Hypersensitivity (urticaria, rash, erythema, burning sensation), chest pain, excessive sweating, clamminess, chills, flushing, fever, myalgia. CV: Palpitations, tachycardia, arrhythmias, hypertension or hypotension, syncope, precordial pain, pulmonary hypertension. GI: Dry mouth, altered taste, nausea, vomiting, abdominal pain, diarrhea, constipation, stomach pain. Endocrine: Gynecomastia. Hematologic: Bone marrow suppression, agranulocytosis, leukopenia. Musculoskeletal: Muscle pain. CNS: Overstimulation, nervousness, restlessness, dizziness, insomnia, weakness, fatigue, malaise, anxiety, euphoria, drowsiness, depression, agitation, dysphoria, tremor, dyskinesia, dysarthria, confusion, incoordination, headache, change in libido. Skin: Hair loss, ecchymosis. Special Senses: Mydriasis, blurred vision. Urogenital: Dysuria, polyuria, urinary frequency, impotence, menstrual upset.


Drug: mao inhibitors, furazolidone may increase pressor response resulting in hypertensive crisis. tricyclic antidepressants may decrease anorectic response. May decrease hypotensive effects of guanethidine.


Absorption: Absorbed from the small intestine. Duration: 4–14 h. Elimination: Primarily in urine. Half-Life: 19–24 h.

Nursing Implications

Assessment & Drug Effects

  • Assess for tolerance to the anorectic effect of the drug. Withhold drug and report to physician when this occurs.
  • Lab tests: Periodic CBC with differential and blood glucose.
  • Monitor periodic cardiovascular status, including BP, exercise tolerance, peripheral edema.
  • Monitor weight at least 3 times/wk.

Patient & Family Education

  • Do not take this drug late in the evening because it could cause insomnia.
  • Report immediately any of the following: Shortness of breath, chest pains, dizziness or fainting, swelling of the extremities.
  • Tolerance to the appetite suppression effects of the drug usually develops in a few weeks. Notify physician, but do not increase the drug dose.
  • Weigh yourself at least 3 times/wk at the same time of day with the same amount of clothing.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2022 Last Updated On: 11/21/2022 (0)
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