For how long should a patient be off of phentermine (anorexiant) before restarting it?

From the Guidelines

Patients should be off phentermine for at least 2-4 weeks before restarting it, allowing the body's receptors to resensitize to the medication. This break is recommended because after using phentermine for 3-6 months, patients often develop tolerance, reducing its effectiveness for weight loss 1. When restarting, begin with the lowest effective dose (typically 15-30mg daily) and monitor for side effects like increased heart rate, elevated blood pressure, insomnia, or anxiety.

Key Considerations

• Patients with cardiovascular disease, uncontrolled hypertension, hyperthyroidism, glaucoma, or a history of drug abuse should avoid phentermine altogether 1.
• Phentermine is approved only for short-term use (up to 12 weeks) and should be part of a comprehensive weight management plan including diet and exercise 1.
• The recommended dosage of phentermine is 15 to 37.5 mg orally once daily in the morning, with low-dose phentermine available as a scored 8-mg tablet that can be prescribed up to 3 times per day 1.

Monitoring and Precautions

• Blood pressure and heart rate should be monitored periodically while taking phentermine 1.
• Patients should be aware of the potential side effects of phentermine, including dry mouth, difficulty sleeping, dizziness, and irritability 1.
• Phentermine should not be used with monoamine oxidase inhibitors or other sympathomimetic amines 1.

From the Research

Phenteramine Restart Guidelines

There is no specific information in the provided studies regarding the exact duration a patient should be off phenteramine before restarting it. However, the studies do provide information on the efficacy and safety of phenteramine use for weight loss.

Efficacy and Safety of Phenteramine

• The study 2 found that longer-term users of phenteramine experienced more weight loss, with patients using continuously for > 12 months losing 7.4% more than the referent group at 24 months.
• The same study 2 also found that the composite CVD or death outcome was rare (0.3%, 41 events), with no significant difference in hazard ratios between groups.
• Another study 3 reported that phentermine/topiramate resulted in a 6.8% weight loss, which is one of the highest among the anti-obesity medications.

Anti-Obesity Medications

• The study 4 mentioned that older medications approved for chronic weight management, including phentermine/topiramate, have not been widely adopted by health care providers, but newer medications like semaglutide 2.4 mg weekly have shown more promise in producing significant weight loss.
• The study 5 compared the efficacy and tolerability of five newer anti-obesity medications, including phentermine-topiramate combination, and found that it had the best Number Needed to Treat (NNT) value of 3.

Considerations for Phenteramine Use

• The study 6 noted that weight loss medications, including phenteramine, can be an effective adjunct to lifestyle modifications in individuals with obesity, but evidence is limited regarding their effect on blood pressure.
• The study 3 emphasized that drug therapy should be initiated in obese individuals after weighing its benefits and risks, and that anti-obesity medications should be tailored for specific patients depending on their chronic conditions, comorbidities, and preferences.