Long-Term Use of Phentermine for Weight Loss: A Study Overview

FDA Approval and Short-Term Use

The weight-loss medication phentermine has been approved by the U.S. Food and Drug Administration (FDA) for short-term use. Researchers aimed to analyze the safety and effectiveness of long-term phentermine use. While lifestyle changes can assist individuals with obesity in losing weight, these interventions typically result in only 5-10% weight loss after six months. Additionally, approximately one-third of individuals may not respond to lifestyle modifications, and many tend to regain lost weight. For those struggling to lose weight, weight-loss medications like phentermine may offer a viable strategy.

Understanding Phentermine’s Mechanism

Phentermine functions primarily as an appetite suppressant. Approved nearly 60 years ago, most research concerning phentermine has focused on treatment durations of less than 12 weeks. Concerns regarding the potential risks associated with long-term use have limited its application to short periods.

Study Design and Participant Groups

Research by Wake Forest School of Medicine

Researchers from the Department of Epidemiology and Prevention at Wake Forest School of Medicine undertook a study to compare the effects of short-term and long-term phentermine use. The primary objectives were to assess weight loss outcomes and cardiovascular disease and mortality rates between different treatment durations. The findings were published in the journal Obesity.

Formation of Patient Groups

Participants were divided into four groups based on their phentermine usage. The first two groups consisted of individuals taking phentermine continuously: one group for 16 weeks or less (short-term continuous) and the other for over 365 consecutive days (long-term continuous). The remaining two groups were categorized based on intermittent use. The short-term intermittent group included individuals with multiple therapy episodes, none lasting more than 16 weeks, while the medium-term intermittent group had at least one episode exceeding 16 weeks.

Findings on Weight Loss and Safety

Weight Loss Results

The study’s results indicated that long-term phentermine treatment was associated with significantly greater weight loss. At six, 12, and 24 months post-treatment, weight loss was notably higher in the long-term, short-term intermittent, and medium-term intermittent groups compared to the FDA-approved short-term group. Specifically, at the six-month mark, the short-term intermittent group outperformed the short-term continuous group, while the medium-term intermittent group demonstrated the most significant weight loss at both six and 12 months. After two years, the long-term continuous group exhibited the highest weight loss among all groups.

Cardiovascular Risks and Safety

The study also evaluated the safety of long-term phentermine use. Concerns primarily centered around cardiovascular side effects and mortality risks associated with extended treatment periods. Although a mild increase in heart rate was noted among phentermine users, heart rates returned to normal after discontinuation of the drug. Interestingly, systolic blood pressure was lower in long-term users, likely due to weight loss rather than the medication itself. Importantly, researchers found no significant increase in cardiovascular disease risk or mortality rates in long-term phentermine users.

Limitations and Future Research

Considerations in the Study

Several limitations were identified in this study. Notably, the researchers did not account for other weight-loss interventions participants might have been engaged in, making it difficult to determine the sole impact of phentermine. Additionally, the cohort of long-term continuous phentermine users was relatively small compared to other groups. Consequently, further research is necessary to evaluate the safety and effectiveness of phentermine among larger populations and over extended treatment periods.

Conclusion: Phentermine as a Weight Loss Option

Potential for Long-Term Use

As many seek safe weight-loss solutions that yield lasting results, phentermine appears to be a promising option. Despite the limitations of this study, findings suggest that phentermine can be safe and effective for treatment durations exceeding three months. Over time, patients experienced greater weight loss without a corresponding increase in cardiovascular risks or mortality. While additional studies are warranted to validate these long-term outcomes, phentermine may represent a reasonable choice for individuals with low cardiovascular disease risk.

Author Information

Written by Jessica Caporuscio, PharmD

References

Lewis KH, Fischer H, Ard J, et al. Safety and Effectiveness of Longer-Term Phentermine Use: Clinical Outcomes from an Electronic Health Record Cohort. Obesity (Silver Spring). 2019
Phentermine: MedlinePlus Drug Information. (n.d.). Retrieved April 3, 2019, from https://medlineplus.gov/druginfo/meds/a682187.html