A groundbreaking study has revealed that thousands of patients using popular GLP-1 weight-loss drugs such as Wegovy and Mounjaro may be experiencing underreported side effects not widely captured in clinical trials.

Researchers analyzed more than 400,000 posts from online forums and identified patient-reported symptoms including irregular menstrual cycles, chills, hot flushes, and fever-like sensations.

These findings highlight a growing gap between controlled clinical trial data and real-world experiences of patients using the medications.

The research also found that about 44 percent of users reported at least one side effect, with gastrointestinal issues such as nausea and stomach pain being the most common, followed by fatigue.

Additionally, around four percent of users reported menstrual irregularities, including missed periods, heavy bleeding, and cycle changes. With approximately 1.6 million people currently using GLP-1 medications in the UK, a number projected to rise to 3.3 million, researchers say the scale of use makes monitoring these emerging symptoms increasingly important.

Emerging Side Effects Raise Monitoring Concerns

Beyond digestive issues, users frequently reported sudden body-temperature fluctuations, including chills, feeling unusually cold, and unexpected hot flushes. These symptoms are believed to potentially relate to how GLP-1 drugs interact with hormonal regulation and appetite-control mechanisms in the brain.

While these reports do not confirm a direct causal link, researchers has revealed that such patterns appearing across large user groups warrant further clinical investigation.

The growing use of GLP-1 medications adds urgency to these findings. Semaglutide, introduced as a weight-loss treatment in the UK in 2018, has recorded about 10.2 million prescriptions over five years.

Most users are believed to access the drugs privately rather than through public healthcare, with usage projected to double between 2024 and 2025.

As adoption rises globally, researchers stress that real-world patient data could play a crucial role in identifying lesser-known side effects and improving long-term safety monitoring.