Phentermine is a prescription appetite suppressant used as a short-term aid in weight management. It works by stimulating the central nervous system, which helps decrease hunger and increase feelings of fullness. While the active ingredient remains the same, phentermine is commonly manufactured in two distinct forms: compressed tablets and encased capsules. Understanding the differences between these two formulations is important, as they vary significantly in appearance, available dosing, and how the drug is released into the body.
Physical Appearance and Available Strengths
Phentermine tablets are typically solid, compressed, and often feature a score line down the middle, which indicates they may be split. These tablets are generally uniform in appearance, sometimes white or featuring blue speckles, and are designed to be swallowed whole. In contrast, the capsule form is encased in a hard gelatin shell that holds either a powder or tiny drug-containing micro-pellets.
The physical difference in form corresponds to a difference in available strengths and dosing flexibility. Phentermine tablets are most frequently manufactured in a 37.5 mg strength, offering a single high-end dose. Capsules provide a wider selection of available strengths, such as 15 mg, 30 mg, and 37.5 mg. This broader range allows a physician more flexibility in titrating the dose to a patient’s specific needs.
Drug Delivery: Immediate vs. Extended Release
The most significant distinction between the two formulations lies in their mechanism for drug delivery. Phentermine tablets are typically formulated for immediate release (IR), meaning the entire dose is designed to dissolve and be absorbed relatively quickly after ingestion. This immediate absorption leads to a rapid peak concentration in the bloodstream, occurring relatively early in the day.
This quick peak concentration provides a strong initial appetite-suppressing effect but means the drug’s presence may taper off sooner. Many phentermine capsules, however, are specifically engineered as an extended-release (ER) formulation. The ER mechanism is often achieved by packaging the drug into micro-pellets within the capsule shell, each designed to dissolve at a different rate.
These varying dissolution rates allow the active ingredient to be released slowly and steadily over an extended period, often lasting 10 to 12 hours. This sustained delivery maintains a more consistent therapeutic level throughout the day. This steady-state concentration helps manage appetite more uniformly, requiring only a single dose taken early in the morning. The choice between the two forms depends on whether a patient requires an intense initial effect or a more prolonged, even effect across the day.
Patient Considerations and Usage Differences
The structural differences between the tablet and capsule forms have direct practical implications for usage. Scored immediate-release tablets can sometimes be split, allowing for a lower or divided dose, though this must always be confirmed with a healthcare professional or pharmacist. Splitting the tablet is possible because the drug is distributed evenly throughout the compressed material.
Extended-release capsules, conversely, must be swallowed whole to preserve the integrity of the release mechanism. Crushing, chewing, or opening an ER capsule would destroy the micro-pellets and cause the entire dose to be absorbed all at once, effectively converting it into an immediate-release dose. This could lead to an unsafe peak concentration of the drug and shorten the duration of its effect, defeating the purpose of the ER formulation.
Another consideration involves the inactive ingredients used to manufacture the medication. Tablets contain various binders and fillers to maintain their compressed shape, while capsules utilize a shell, most often made of gelatin. Patients with specific allergies, dietary restrictions, or religious concerns regarding animal products, such as gelatin, may need to opt for the tablet form.
While the active drug is identical, the cost to the patient can sometimes vary between the two forms. Factors such as generic availability, the presence of a brand-name extended-release formulation, and insurance coverage influence the final out-of-pocket price. Patients should consult their pharmacy to compare the costs of the tablet and capsule options.