From the Guidelines
When restarting phentermine in a patient who previously took 37.5 mg but stopped for several months, it's recommended to begin with a lower dose of 15 mg daily and gradually titrate back up to the previous 37.5 mg dose over 1-2 weeks. This approach is based on the most recent and highest quality study available, which emphasizes the importance of cautious dose escalation to minimize potential side effects 1. The recommended dosage of phentermine is 15 to 37.5 mg orally once daily in the morning, as stated in the study published in Gastroenterology in 2017 1.
Key Considerations
- The patient should take the medication in the morning to avoid sleep disturbances, with or without food.
- During the titration period, the patient should monitor for side effects and effectiveness.
- If side effects occur, slowing the titration is appropriate.
- This cautious restart approach is recommended because tolerance to phentermine may have decreased during the months off the medication, making the patient more sensitive to both therapeutic effects and side effects.
- Additionally, the patient should be reminded that phentermine is approved for short-term use (typically up to 12 weeks) as an adjunct to lifestyle modifications including diet and exercise for weight management.
Potential Side Effects
- Increased heart rate
- Elevated blood pressure
- Insomnia
- Anxiety
- Dry mouth
- Difficulty sleeping
- Dizziness
- Irritability
Special Clinical Considerations
- Phentermine should not be used with monoamine oxidase inhibitors or other sympathomimetic amines.
- Patients who have anxiety or insomnia might feel their condition is exacerbated by phentermine, and would not be ideal candidates.
- Caution is advised in patients with a history of cardiovascular disease or uncontrolled hypertension.
From the FDA Drug Label
2.1 Exogenous Obesity Dosage should be individualized to obtain an adequate response with the lowest effective dose. The usual adult dose is 15 mg to 30 mg at approximately 2 hours after breakfast for appetite control.
The FDA drug label does not answer the question.
From the Research
Phentermine Dosing After Cessation
When a patient has previously taken 37.5 mg of phentermine and stops for several months, the dose to restart is not explicitly stated in the provided studies. However, we can look at the general information about phentermine dosing and cessation:
- There is no direct evidence from the studies 2, 3, 4, 5, 6 that provides a specific recommendation for the dose to restart phentermine after a patient has stopped taking it for several months.
- A study on abrupt phentermine cessation 6 suggests that stopping phentermine does not induce amphetamine-like withdrawal, and symptoms after cessation may represent the loss of therapeutic effect rather than withdrawal.
- The studies provided do not offer guidance on how to restart phentermine after a period of cessation, including the appropriate dose.
Considerations for Restarting Phentermine
Some key points to consider when thinking about restarting phentermine, although not directly answering the dosing question, include:
- Phentermine is used for the short-term management of obesity, and long-term use may be associated with severe cardiovascular side effects, abuse, and dependence 4.
- The drug has been shown to be effective for weight loss in various populations, including pediatric patients 2 and adults 3, when used as part of a weight management program.
- Potential drug-drug interactions should be considered when prescribing phentermine, especially in patients taking other medications concurrently 4.
Lack of Direct Evidence
Given the information available, there are no research papers among those provided that directly assist in answering the question of what dose of phentermine to restart in a patient who previously took 37.5 mg and stopped for several months.