Symptoms that patients discuss with one another online and may never mention to a doctor or report to regulators have now been counted at scale. University of Pennsylvania researchers used large language models to analyze 410,198 Reddit posts from May 2019 through June 2025 that mentioned semaglutide or tirzepatide. They identified 67,008 users who said they were taking the medications, and 43.5% of those users described at least one side effect.
The study, published in April in Nature Health, flagged two categories that may not be fully reflected in clinical trial data or current drug labeling: reproductive symptoms, mainly menstrual changes, and temperature-related complaints such as chills, feeling cold, hot flashes, and fever-like symptoms. Fatigue was the second most common complaint overall, even though it reached reporting thresholds in relatively few clinical trials.
