Phentermine: The Obesity Medication with the Most Side Effects in Korea

A detailed pharmacovigilance investigation conducted by Kyung Hee University and Ajou University aimed to identify predictors associated with an increased risk of serious adverse events (SAEs) related to anti-obesity medications and to provide crucial evidence on drug safety.

The Study

The study analyzed 13,766 side effect reports from 2010 to 2019, uncovering important insights into the prevalence and seriousness of adverse drug events (ADEs) related to these medications ( 1 ).

The average age of patients reporting side effects was 41, with a significant majority (89.02 percent) being female. Out of these reports, 4,168 cases were either confirmed or likely linked to weight loss medications, indicating a significant impact on patient health.

Phentermine and Saxenda at the Forefront of Side Effects Reports

Among the anti-obesity medications, phentermine was the most commonly reported causative agent, accounting for 33.2 percent (1,385 cases), followed by Saxenda (liraglutide) at 27.7 percent (1,155 cases).

The study highlighted that ADEs associated with psychiatric disorders, liver and biliary system disorders, cardiovascular disorders, and respiratory disorders were more likely to be serious.

Men were more likely to experience ADEs related to gastrointestinal disorders and less likely to have heart and rhythm disorders, reflecting gender-specific risk profiles. The common side effects reported included gastrointestinal disorders (29.1 percent), central and peripheral nervous system disorders (19.2 percent), and mental disorders (16.9 percent).

However, severe cases most frequently involved mental disorders (25.7 percent) and nervous system disorders (19 percent), with 30 percent of the severe mental disorders attributed to phentermine.

The research team stated that the risks of severe side effects stemming from Phentermine and Saxenda were quite high, with patients taking the drug 1.73 times more likely to experience mental disorders, 4.57 times more likely for respiratory issues, 5.70 times more likely for cardiovascular problems, and a staggering 22.95 times more likely for liver and bile duct disorders compared to those not taking the drug.

An alarming 16 percent of patients were found to be using two or three anti-obesity drugs simultaneously, significantly increasing the risk of side effects.

The Crucial Need for Vigilance in Managing Phentermine Therapy

Given these findings, the study emphasized the need for ongoing pharmacovigilance investigation and monitoring to enhance awareness of ADEs induced by anti-obesity medications.

The particular focus on phentermine, due to its prevalence as a causative medication in reported ADE cases, highlights the importance of vigilant surveillance and evaluation to ensure the safety and efficacy of these medications.


The comprehensive analysis of real-world data from this study has shed new light on the prevalence and seriousness of adverse drug events related to anti-obesity medications, particularly phentermine.

By identifying predictors associated with an increased risk of serious adverse events, the findings reinforce the critical need for ongoing pharmacovigilance to ensure the safe use of anti-obesity medications and to mitigate potential risks associated with their use. This includes a keen focus on gender-specific risks and the compounded risks associated with multiple medication use.

  1. Lee, J. H., Kim, Y., Lee, J. Y., Yoon, S., Kim, M. J., & Kang, W. (2023). Pharmacovigilance of Anti-Obesity Medications in Korea: A Cross-Sectional Study of Spontaneously Reported Adverse Drug Events. Journal of Global Health, 13, 04095.