As National Obesity Week approaches, the treatment conversation is increasingly about matching the right intervention to the right patient. Within an expanding therapeutic landscape, phentermine retains a defined role as an adjunct to a medically monitored programme of nutrition, physical activity, and behaviour change.¹,²,³
Obesity is now understood as a chronic, complex disease rather than simply a consequence of individual behaviour. Contemporary guidance emphasises comprehensive care that addresses health goals, nutrition, physical activity, psychological factors, obesity-related complications, and, where appropriate, pharmacotherapy or metabolic and bariatric surgery.²,³
The growth of obesity pharmacotherapy has widened the range of options available to clinicians, but it has also made individualisation more important. Treatment choice needs to take account of the patient’s clinical profile, treatment goals, tolerability, access, affordability, and the regulatory indication of the medicine being considered.²,³,⁴
In South Africa, phentermine occupies a specific place within this landscape. The current approved Professional Information identifies phentermine as an anorectic agent for the management of obesity and indicates it as a short-term adjunct to a medically monitored comprehensive weight-reduction regimen based on measures such as exercise, energy restriction, and behaviour modification.¹
That short-term positioning matters. The 2025 South African obesity guideline notes that phentermine is registered locally for short-term treatment only.² The Professional Information states that patients require medical review after a defined course of treatment, which ideally should not exceed three months.¹ In practice, this gives clinicians a clear point at which to assess treatment response, tolerability and whether the patient’s goals remain appropriate.¹,²
The next step should be determined by the patient’s response and ongoing clinical needs.¹,²
Who is the appropriate patient?
The appropriate patient is not defined by weight alone. According to the approved Professional Information, treatment is intended for patients with obesity who have not achieved an adequate clinical response to an appropriate weight-reducing regimen alone. The labelled threshold is a body mass index (BMI) of 30kg/m² or higher, although treatment may be initiated at a lower BMI in patients with other risk factors.¹
The Professional Information also states that secondary organic causes of obesity should be excluded before prescribing.
Phentermine acts primarily through sympathomimetic pathways that reduce appetite.¹,² A 2024 review focused specifically on phentermine concluded that contemporary observational evidence supports clinically meaningful weight loss in adults, while also highlighting that the evidence base for long-term monotherapy remains substantially less robust than for newer chronic weight-management medicines. This distinction supports the importance of remaining within locally approved use.⁴
Short-term treatment can still have a purpose
The increasing emphasis on chronic obesity management does not eliminate the clinical value of a time-limited intervention. A defined short-term course can be used to support early weight reduction while patients continue the dietary, activity, and behavioural components of a comprehensive programme. The aim is not to position medication as a substitute for these measures, but as an adjunct where lifestyle intervention alone has produced an inadequate clinical response.¹,²
Recent international standards continue to recognise phentermine as a short-term obesity medicine. The American Diabetes Association’s 2025 Standards of Care lists phentermine among sympathomimetic anorectic agents approved for short-term use and reports clinically meaningful weight reduction in trial data, while emphasising the need for appropriate patient selection and clinical monitoring.⁵
This can be particularly relevant when the clinical objective itself is time limited. Rather than asking whether a short-term medicine can fulfil the role of long-term obesity therapy, the more useful question is whether it can contribute meaningfully to a clearly defined short-term treatment goal in an appropriately selected patient.¹,⁴,⁵
A potential bridge before surgery
Pre-operative weight reduction is one setting in which a defined treatment window may be clinically useful. A 2025 narrative review found that weight loss before metabolic and bariatric surgery may reduce body weight and liver size and may contribute to easier operative conditions, although the authors stressed that optimal pharmacological protocols still require stronger evidence.⁶
More specifically, a 2025 prospective, randomised, placebo-controlled trial evaluated low-dose phentermine as a pre-operative intervention in patients undergoing Roux-en-Y gastric bypass or sleeve gastrectomy. After 14 weeks, participants receiving phentermine achieved greater mean weight loss than those receiving placebo. These findings support a potential role for phentermine in pre-operative weight reduction, while any clinical use of Phentermine should remain aligned with its approved Professional Information.⁷
Earlier real-world evidence also supports the concept of pharmacotherapy around bariatric surgery. In a 2023 study of patients with a BMI above 60kg/m², pre-operative use of phentermine and/or topiramate was associated with greater total body-weight loss at one year than observed in patients who did not receive anti-obesity medication during the first postoperative year. However, the phentermine-topiramate combination is not available in South Africa.² These findings support further investigation of pharmacotherapy as part of carefully selected pre-operative pathways.⁸
Affordability remains part of the treatment decision
Access is an increasingly important part of obesity care. The South African guideline explicitly identifies cost, along with efficacy, safety, tolerability, medication interactions, and mode of administration, as a consideration when selecting obesity pharmacotherapy. This is especially relevant in settings where patients fund medicines out of pocket or where access to newer therapies is limited.²
Economic research reinforces the scale of this access challenge. A 2023 analysis of anti-obesity medicine prices found substantial differences between market prices and estimated minimum manufacturing prices and concluded that affordability remains a major barrier to treatment access. Although that analysis did not evaluate Phentermine specifically, it illustrates why cost cannot be separated from real-world treatment selection.⁹
For clinicians, this makes therapeutic choice more than a comparison of efficacy figures. An intervention must be clinically appropriate, accessible, and realistic for the individual patient. Phentermine’s established oral, short-term treatment model may therefore remain relevant for selected patients who meet the approved criteria and require a medically supervised adjunct to their weight-reduction programme.¹,²,⁴
A defined place in a changing landscape
Obesity treatment will continue to evolve, but a broader therapeutic landscape does not mean that every patient requires the same intervention. Current evidence increasingly supports a personalised approach in which health needs, treatment goals, clinical characteristics, access, and patient preferences guide treatment selection.²,³
For Phentermine, the role is deliberately focused: short-term adjunctive treatment within a medically monitored comprehensive programme for appropriately selected patients who have not achieved an adequate response to a weight-reducing regimen alone. Used within that framework, phentermine remains one option in the clinician’s obesity-management toolkit.¹,²
National Obesity Week provides an opportunity to move the conversation beyond weight alone and towards evidence-based, individualised obesity care. The central message is not that one medicine fits every patient, but that effective care depends on matching the intervention to the person, the clinical objective, and the appropriate treatment window.²,³
In practice, this reinforces a broader principle of modern obesity care: pharmacotherapy should follow clinical assessment and form part of a structured treatment plan rather than being used as an isolated weight-loss intervention.¹,²,³