Concerns about weight-loss drugs: what evidence supports claims of side effects like nausea and hair loss?

Popular weight-loss medications like Wegovy and Mounjaro have become increasingly well-known, and with their rise in popularity have come numerous reports of various side effects. Recently, researchers have suggested that GLP-1 medications might be linked to hair loss.

It can be challenging to determine which of these reported outcomes have been thoroughly investigated by experts and which are merely rumours. This article examines some of the most discussed side effects, exploring which have scientific backing and which remain unproven.

Nausea, vomiting, diarrhoea, and constipation are commonly reported gut-related problems by users of GLP-1 medications. While these symptoms are uncomfortable, they are widely recognised and have been documented in clinical trials. Experts explain that these side effects may be related to how the drugs function: they slow down the digestive process, delay stomach emptying, and influence signals between the gut and the brain.

Due to strong evidence supporting these side effects, they are listed as very common in patient information leaflets. Manufacturers typically note that these symptoms usually diminish over time.

Several eye conditions have been associated with GLP-1 medications. Last year, a study indicated that individuals with diabetes using these drugs might have double the risk of developing age-related macular degeneration. Additionally, reports from adverse event systems and matched cohort studies suggest that some GLP-1 medications could potentially lead to a condition called non-arteritic anterior ischaemic optic neuropathy, which can cause sudden and permanent vision loss.

Pharmaceutical companies acknowledge this as a possible side effect for certain GLP-1 medications, and it is mentioned in the patient leaflets for drugs like Wegovy. However, experts emphasize that this condition is extremely rare.

There have been many reports of unexpected pregnancies among individuals using GLP-1 medications. Consequently, women have been advised to use effective contraception alongside these drugs. Experts suggest plausible, though unconfirmed, reasons for this, such as GLP-1 medications potentially interfering with the effectiveness of oral contraceptives or increasing fertility in women due to their weight-loss effects.

However, conclusive research in this area is limited. This is partly because pregnancy or the intention to become pregnant were exclusion criteria in the initial clinical trials for these drugs. Research into whether GLP-1 medications affect male fertility is also in its early stages. Experts also point out that unplanned pregnancies occur regularly among women using oral contraceptives who are not taking GLP-1 medications.

The UK's Medicines and Healthcare products Regulatory Agency has stated that GLP-1 medicines should not be taken during pregnancy or when trying to conceive, citing insufficient safety data to determine potential harm to a baby. Similar warnings are included in patient information leaflets.

Social media platforms are filled with accounts of people experiencing significant changes in their facial appearance after using GLP-1 medications, including sunken eyes, wrinkles, and sagging skin. Although not listed in patient information, surgeons recognise these changes as a consequence of rapid weight loss. This effect is not exclusive to specific GLP-1 drugs and can also result from other methods that lead to substantial weight reduction.

Hair loss gained attention this week following research suggesting a possible link with the use of GLP-1 medications in adults with type 2 diabetes. A potential connection has been mentioned before, with patient leaflets for Mounjaro and Wegovy listing it as a common side effect. Experts have previously called for more research into this area.

While the exact mechanisms are still speculative, one theory is that such hair loss is caused by rapid weight loss—and the associated metabolic changes and nutritional deficiencies—rather than the medications themselves. Studies indicate that hair loss is a frequent complication following bariatric surgery and has also been observed in individuals undergoing extreme diets.

The latest study did not investigate whether the hair loss was reversible. However, the researchers suggest their findings indicate that the observed association is mainly due to non-scarring types of alopecia, such as telogen effluvium, which are often reversible.

The term Ozempic foot describes a bony appearance of the feet, sometimes accompanied by pain, claimed to be a side effect of GLP-1 medications, though it is not listed in patient information leaflets. While studies are scarce, it appears that rapid weight loss, by any method, can affect the feet. Podiatrists have noted this can include a loss of soft tissue, where reduced fat padding can diminish cushioning in the heels and balls of the feet, leading to pain.

One study found that a type of weight loss surgery, sleeve gastrectomy, was linked to a decrease in shoe size one year later.