Phentermine
ADIPEX-P
What it isSympathomimetic norepinephrine releaser; short-term obesity treatment.
Why this oneIt is the inexpensive, widely used single-agent stimulant option for appetite suppression.
What limits itBlood pressure and heart rate rise; it is Schedule IV and short-term only. Avoid cardiovascular disease and MAOIs.
FDA-approved for
- short-term obesity (1959)
FDA label
Read the full label on DailyMed ↗
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Exogenous obesity — short-term (a few weeks) adjunct to exercise, behavioral modification, caloric restriction (BMI >=30, or >=27 with risk factors) | Adult (>16 yr) | 37.5 mg QD before breakfast or 1-2 h after; 18.75 mg QD may suffice | Lowest effective dose (18.75 mg QD-BID or 37.5 mg QD) | 37.5 mg QD |
Renal Severe impairment (eGFR 15-29): max 15 mg QD; avoid if eGFR <15 or dialysis
Hepatic Undefined
Short-term use only (a few weeks); tolerance to anorectic effect usually develops within a few weeks
Instructions
- Take before breakfast or 1-2 hours after breakfast; with or without food
- Avoid late-evening dosing (insomnia)
- Individualize to lowest effective dose; do not exceed recommended dose if tolerance develops — discontinue instead
- Not recommended in pediatric patients <=16 yr
Contraindications
- History of cardiovascular disease (coronary artery disease, stroke, arrhythmias, congestive heart failure, uncontrolled hypertension)
- MAOIs (concurrently or within 14 days) due to risk of hypertensive crisis
- Hyperthyroidism
- Glaucoma
- Agitated states
- History of drug abuse
- Pregnancy
- Nursing
Cautions
- Primary pulmonary hypertension (rare, frequently fatal) — discontinue for new dyspnea, angina, syncope, or lower-extremity edema
- Serious regurgitant cardiac valvular disease (rare)
- Coadministration with other weight-loss drugs (incl. SSRIs/serotonergic agents) not recommended — safety not established
- Abuse and dependence (amphetamine-related, C-IV); prescribe smallest feasible quantity
- Tolerance develops within a few weeks — discontinue rather than exceed dose
- May impair ability to drive or operate machinery
- Caution in even mild hypertension (may raise BP)
- Insulin/oral hypoglycemic requirements may decrease
- Alcohol may cause adverse drug reaction
Adverse reactions
- CV: palpitation, tachycardia, elevated BP, ischemic events; rare pulmonary hypertension/valvulopathy
- CNS: overstimulation, restlessness, insomnia, dizziness, euphoria/dysphoria, tremor, headache, psychosis
- GI: dry mouth, unpleasant taste, diarrhea, constipation
- Urticaria; impotence, changes in libido
Pregnancy Contraindicated (Category X) — weight loss offers no benefit and may cause fetal harm.
Lactation Contraindicated in nursing; discontinue drug or discontinue nursing (other amphetamines present in milk).
NO BOXED WARNINGS
Principal riskBlood pressure and heart rate rise; short-term use only
Cost, est. cash$50–$1,400/month
Generic entry1982
Classes and tags
Clinical profile
Legacy pregnancy categoryUnknown / historical label unavailable
Defining liabilityGenerally tolerated at therapeutic doses; clinically important risks are agent-specific and increase with interactions or organ impairment.
Mechanism of action: Phentermine ballicule
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