Researchers have identified what they believe could be lesser-known side effects of taking weight loss jabs, with 44 per cent of people polled, reporting at least one symptom.
All medicines can come with side effects, ranging from relatively mild issues such as headaches or stomach discomfort to rarer complications that are more serious.
With many long-established drugs, those reactions tend to be well documented over time, as widespread use gives researchers clearer insight into how people are affected.
But GLP-1 medications may be a different case, largely because their use for weight loss has expanded rapidly and relatively recently.
As more people take these injections, new patterns can emerge depending on factors like age, starting weight, other prescriptions, and existing health conditions.
A fresh study aims to shed more light on what some users say they are experiencing.
Academics from Penn Engineering reported that semaglutide (used in Ozempic and Wegovy) and tirzepatide (used in Mounjaro and Zepbound) may be associated with effects that aren’t always highlighted in typical discussions about these drugs.
Using AI, the team reviewed around 400,000 Reddit posts made by more than 70,000 users over the past five years to identify recurring themes in what people reported about weight-loss and type 2 diabetes medications.
In their analysis, 44 per cent of posters described at least one issue, including menstrual changes, chills, hot flashes, and other symptoms.
The most frequently mentioned complaints were gastrointestinal problems and fatigue, followed by chills, hot flashes, and sensations similar to developing a fever.
The researchers noted that these medications act on brain pathways involved in hormone regulation—including the hypothalamus—which could help explain certain reports, but they argue there should be more recognition of the range of symptoms patients may notice.
Lyle Ungar, a co-author on the study, said clinical trials ‘generally identify the most dangerous side effects of drugs’, but they ‘fail to find what symptoms patients are most concerned about’ which has been seen in a ‘large collection of posts’ citing side effects previously not commonly associated with the drugs.
Sharath Chandra Guntuku, the study’s author, explained that the side effects were written by users online ‘unprompted’, and that ‘clinicians could potentially pay attention to them.’
The study also noted that four per cent of Reddit users described menstrual irregularities such as heavier bleeding, missed periods, or changes in cycle length—symptoms that can also occur with conditions including polycystic ovary syndrome (PCOS) and thyroid disorders such as hypothyroidism.
It further suggested that men were more likely than women to report side effects in the posts reviewed.
Guntuku added: “Clinical trials are the gold standard, but by design, they are slow. This is not a replacement for trials, but it can move much faster, and that speed matters when a drug goes from niche to mainstream almost overnight.”