Phentermine Tablets vs Capsules: No Clinically Meaningful Difference
There is no clinically significant difference in efficacy or safety between phentermine tablets and capsules—both formulations deliver the same active ingredient and produce equivalent therapeutic effects for weight loss. 1
Formulation Equivalence
Both tablets and capsules contain the same active ingredient (phentermine hydrochloride) and are bioequivalent, meaning they deliver the medication to your body in the same way 1
The FDA-approved dosing for phentermine monotherapy is 15 mg to 30 mg daily, regardless of whether it's administered as a tablet or capsule 1
The choice between tablet and capsule is purely a matter of patient preference for swallowing and has no impact on clinical outcomes 1
Critical Context for Your Patient
For your 49-year-old patient with prior phentermine/topiramate experience, the more important consideration is whether to use phentermine monotherapy versus the FDA-approved combination product (Qsymia).
Combination Therapy Superiority
The phentermine/topiramate extended-release combination (available only in capsules) demonstrates superior weight loss compared to phentermine alone: 7.8% weight loss at 7.5/46 mg dose and 9.8% at 15/92 mg dose versus 1.2% with placebo 2, 3
The American Gastroenterological Association recommends the combination product as first-line pharmacotherapy for patients with BMI ≥30 kg/m² or ≥27 kg/m² with weight-related comorbidities 4, 2
The combination formulation provides sustained efficacy with persistent weight loss at 108 weeks (9.3% and 10.5% at the two higher doses) 2
Dosing Protocol for Combination Therapy
Start with phentermine/topiramate ER 3.75/23 mg daily for 14 days, then increase to 7.5/46 mg daily as maintenance 4, 3
If less than 3% weight loss at 12 weeks, escalate to 11.25/69 mg for 14 days, then to maximum dose of 15/92 mg daily 4, 3
Discontinue if less than 5% weight loss after 12 weeks on maximum dose 4, 3
Safety Monitoring Requirements
Monitor blood pressure and heart rate at each visit, as phentermine can cause modest increases in heart rate despite generally favorable blood pressure effects 4, 5
For women of childbearing potential, obtain pregnancy test before initiation and consider monthly testing, as topiramate carries teratogenicity risk (orofacial clefts) 4, 3, 6
Avoid in patients with cardiovascular disease history, uncontrolled hypertension, hyperthyroidism, or glaucoma 1
Schedule monthly visits for the first 3 months, then every 3 months thereafter 3
Common Pitfall to Avoid
Never abruptly discontinue phentermine/topiramate ER—taper by taking one capsule every other day for at least 1 week before stopping to minimize seizure risk 4, 3, 6
Phentermine monotherapy is FDA-approved only for short-term use (a few weeks), though it is commonly used chronically off-label 1, 5
The combination product should not be used with other weight loss medications, SSRIs, or MAOIs 1