Semaglutide-based medications, particularly Wegovy, are associated with a rare side effect that leads to vision loss. The condition also appears to affect men more than women.
The expression “ocular stroke” recently appeared in reports about a very rare side effect of weight loss injections. This is not a formal medical diagnosis, but rather an abbreviation used to describe a condition in which reduced blood flow damages the optic nerve and causes sudden loss of vision.
The expression can be misleading. Unlike a conventional stroke – which can lead to loss of the ability to move limbs or speak – an eye stroke can be more difficult to recognize initially. THE vision may be lost in whole or in partin one or both eyes, without numbness or paralysis.
The word “stroke” is used because, as with the most well-known condition, the underlying cause is loss of blood supply which leads to cell death and tissue damage. The correct medical term for ocular stroke is non-arteritic anterior ischemic optic neuropathy (NAION).
The recent association between NOIAA and weight loss treatments gained prominence following a large study that looked at semaglutide, the active ingredient in several popular weight loss medications.
The researchers analyzed more than 30 million side effects reported to the US Food and Drug Administration (FDA) and found that 31,774 involved semaglutide. One medicine in particular stood out: Wegs showed a much stronger association with anterior ocular nerve ischemic optic neuropathy (AION) than other semaglutide-based treatments.
The study suggested that the risk of ocular stroke associated with Wegovy was almost five times higher to that associated with Ozempic, although Wegovy is linked to fewer reported side effects overall.
To understand why semaglutide may reduce blood flow to the eyes, a little context is needed. Semaglutide is a synthetic version of a natural hormone called GLP-1, which helps regulate blood sugar. It does this by stimulating the production of insulin, reducing the release of a hormone that raises blood sugar, glucagon, and slowing digestion.
Semaglutide has been used to treat type 2 diabetes, heart disease, and obesity. Wegovy is administered by injection at a higher maximum dose than Ozempic, another injectable medication. Injectable medications enter the bloodstream more quickly and in higher concentrations than tablets – and, remarkably, no link was found between Naion and Rybelsus, the tablet form of semaglutide.
The rapidity with which Wegovy causes weight loss – faster than other treatments – may be part of the explanation. The human body is a delicately balanced system in which no organ or process functions in isolation. The autonomic nervous system, which controls involuntary functions such as heart rate and digestion, depends on hormonal balance necessary to keep everything under control. When an external medicine significantly alters the behavior of these hormones, it can affect the rest of the body in unexpected ways.
The relatively high doses used with Wegovy can cause fluctuations in blood pressure beyond normal levels. A significant drop in blood pressure reduces the speed at which blood flows through the body, and the eyes are particularly vulnerable to this. The retina is supplied by some of the smallest blood vessels in the body and depends on these small vessels for its oxygen supply. Any significant change in blood pressure can seriously disrupt this delicate circulation.
Men face a much greater risk than women
This, however, does not fully explain why a medication that is broadly beneficial for heart health and blood sugar control can have such a specific detrimental effect on vision. It also doesn’t explain another surprising finding from the study: Men who take these weight-loss treatments appear to face a three times greater risk of vision loss compared to women.
The study did not provide enough details about the differences between male and female participants. For example, if men with more severe obesity than women were included. Furthermore, large-scale data of this type does not always capture the finer details needed to fully understand the cause and effect relationship.
It’s important to keep all of this in perspective: although a link between semaglutide and vision loss has been identified, this side effect remains rare.
More research is needed to establish safe dosage levels and to understand whether certain factors — such as gender, age, weight or preexisting health conditions — make some people more vulnerable than others. Semaglutide is being prescribed for an increasing range of conditions and, increasingly, to younger patients. To ensure that these treatments do not lead to permanent vision losswell-planned clinical trials that assess the level of risk are essential.
A Novo Nordisk spokesperson told The Guardian: “Patient safety is our top priority and we take any reports of adverse events arising from the use of our medicines very seriously. We work closely with authorities and regulatory bodies around the world to continuously monitor the security profile of our products.”
The EU-issued package inserts for Wegovy, Ozempic and Rybelsus have been updated to include Naion, they added, but “based on the totality of the evidence, we conclude that the data did not suggest the possibility of a causal relationship between semaglutide and Naion and Novo Nordisk believes that the benefit-risk profile of semaglutide remains favorable”.
