When can I administer Adipex (phentermine)?

When to Administer Adipex (Phentermine)

Adipex can be prescribed for patients with BMI ≥30 kg/m² or BMI ≥27 kg/m² with weight-related comorbidities (hypertension, type 2 diabetes, dyslipidemia, obstructive sleep apnea), but only after excluding cardiovascular disease and other absolute contraindications. 1, 2

Patient Selection Criteria

BMI Requirements

• Prescribe phentermine for patients with BMI ≥30 kg/m² without comorbidities 1, 2
• Prescribe for patients with BMI ≥27 kg/m² who have weight-related comorbidities including hypertension, type 2 diabetes, dyslipidemia, or obstructive sleep apnea 1

Absolute Contraindications (Never Prescribe)

• Any history of cardiovascular disease including coronary artery disease, stroke, arrhythmias, congestive heart failure, or uncontrolled hypertension 1, 3, 2
• Current or recent (within 14 days) monoamine oxidase inhibitor (MAOI) use due to risk of hypertensive crisis 4, 2
• Pregnancy or nursing 1, 4, 2
• Hyperthyroidism 4, 2
• Glaucoma 4, 2
• Agitated states or anxiety disorders 4, 2
• History of drug abuse 2
• Known hypersensitivity to sympathomimetic amines 2

Pre-Treatment Assessment

Required Screening Before First Dose

• Measure baseline blood pressure and heart rate 4
• Screen for cardiovascular disease history through detailed history 4
• Assess pregnancy status in all females of reproductive potential and provide contraception counseling 4
• Exclude hyperthyroidism 4
• Screen for glaucoma 4
• Evaluate for agitated states or anxiety disorders 4
• Confirm no MAOI use in past 14 days 4
• Assess renal function (eGFR) 2

Renal Dosing Adjustments

• Maximum dose 15 mg daily for severe renal impairment (eGFR 15-29 mL/min/1.73 m²) 2
• Avoid phentermine entirely in end-stage renal disease (eGFR <15 mL/min/1.73 m²) or dialysis patients 2

Dosing and Administration

Standard Dosing

• Start with 15 mg orally once daily, taken approximately 2 hours after breakfast 2
• May increase to 30 mg daily if needed for adequate appetite suppression 2
• Alternative low-dose regimen: 8 mg up to three times daily (at 1:00 PM and 4:00 PM) to target afternoon/evening eating patterns 4, 5
• Avoid late evening dosing due to insomnia risk 2
• Not recommended for patients under 16 years of age 2

Duration of Treatment

• FDA-approved only for short-term use (up to 12 weeks) 4, 2
• Many practitioners prescribe off-label for longer durations given obesity's chronic nature, but this requires ongoing monitoring 4, 3
• Discontinue if <5% weight loss after 12 weeks on maximum dose 1, 4, 3

Monitoring Requirements

Initial Phase (First 3 Months)

• Monitor blood pressure and heart rate at every visit, at least monthly 1, 4
• Assess efficacy and safety monthly 1

Ongoing Monitoring (Beyond 3 Months)

• Continue blood pressure and heart rate monitoring at every visit 3
• Assess weight loss progress at least every 3 months 1
• Monitor for side effects including dry mouth, insomnia, dizziness, irritability, nausea, constipation 1, 4

Special Populations to Avoid

Cardiovascular Risk Patients

• Do not prescribe phentermine to patients with any cardiovascular disease 1, 3
• Consider orlistat as a safer alternative for patients with cardiovascular concerns, as it works via gastrointestinal lipase inhibition rather than sympathetic activation 1, 4
• Lorcaserin is another safer alternative for cardiovascular patients (though note: lorcaserin was withdrawn from market in 2020) 1

Drug Interaction Concerns

• Avoid combining with other sympathomimetic agents 2, 6
• Do not combine with serotonergic agents (SSRIs like fluoxetine, sertraline, paroxetine) due to lack of safety data 2
• Exercise caution with tramadol (severe drug-drug interaction potential) 6
• Avoid combination with dextromethorphan (moderate interaction) 6

Patient Counseling Points

Setting Expectations

• Phentermine must be combined with lifestyle modifications including reduced-calorie diet, exercise, and behavioral therapy—never use as monotherapy 1, 2
• Inform patients of FDA approval for short-term use only (12 weeks), though off-label longer use is common 4, 3
• Explain that phentermine is a Schedule IV controlled substance, though addiction potential is low when used appropriately 1, 7

Warning Signs Requiring Immediate Discontinuation

• New or worsening dyspnea (potential primary pulmonary hypertension) 2
• Angina pectoris 2
• Syncope 2
• Lower extremity edema 2

Common Pitfalls to Avoid

• Do not prescribe to patients with "stable" or "controlled" cardiovascular disease—any cardiovascular history is an absolute contraindication 1, 3
• Do not continue beyond 12 weeks if inadequate weight loss (<5%) achieved 1, 4, 3
• Do not prescribe late in the day due to insomnia risk 2
• Do not combine with other weight loss medications or serotonergic agents 2
• Do not overlook renal function assessment—dose adjustment required for renal impairment 2