Splitting Phentermine Capsules: Not Recommended
Do not split phentermine capsules to take half the dose, as capsule splitting results in highly unequal drug distribution between the top and bottom portions of the capsule, leading to unpredictable and inaccurate dosing. 1
Why Capsule Splitting Is Problematic
Research demonstrates that when capsules are split, the base consistently contains approximately 75% of the drug powder while the top contains only 25%, creating significant dosing variability that makes accurate half-dosing impossible. 1 This non-uniform distribution means you cannot reliably achieve a consistent half-dose by splitting capsules.
Proper Low-Dose Alternatives
Instead of splitting capsules, use these FDA-approved low-dose formulations:
Start with 8 mg tablets - These are scored and can be split to achieve doses as low as 4 mg, allowing precise dose titration. 2, 3
Use 15 mg capsules - This is the lowest standard capsule dose available and represents an appropriate starting point for many patients. 3
Consider the 8 mg formulation (Lomaira) - This can be dosed up to 3 times daily (approximately 30 minutes before meals) and provides flexibility for lower total daily doses. 2, 3
Recommended Dosing Strategy
The proper approach to low-dose phentermine therapy involves:
Initial dosing: Start at 8-15 mg once daily in the morning, approximately 2 hours after breakfast. 3
Titration: Gradually increase based on efficacy and tolerability, with options including 9.375 mg (quarter tablet), 18.75 mg (half tablet), or split dosing of 18.75 mg twice daily. 3
Maximum dose: Up to 37.5 mg once daily, though lower doses may be adequate for many patients. 3
Clinical Context
Lower doses have demonstrated efficacy in clinical practice. Research shows that phentermine 8 mg twice daily (total 16 mg/day) combined with other agents produced significant weight loss averaging 22.4% of initial weight. 4 Additionally, 15 mg daily resulted in 46% of patients achieving ≥5% weight loss at 28 weeks. 3
The 30 mg dose shows greater initial efficacy at 3 months compared to 15 mg, but by 6 months the difference disappears, suggesting that starting lower and continuing longer may be equally effective with potentially fewer adverse effects. 5
Important Safety Considerations
Timing matters: Avoid late evening dosing due to insomnia risk. 3
Cardiovascular monitoring: Blood pressure and heart rate should be monitored periodically, especially in patients with cardiac risk factors. 6
Duration: While FDA-approved for only 12 weeks, many practitioners use phentermine off-label for longer periods with appropriate documentation and monitoring. 2, 3