By Christopher Piercecchi, MD
Physician and Wellness Manager, Founder, The Men’s Clinic for Wellness & Vitality
SITREP is an evidence-review briefing for patients and colleagues of The Men’s Clinic for Wellness & Vitality. It is educational and does not constitute individualized medical advice.
Many of you have asked me specific questions about GLP-1 medications, so I thought I would give you a quick update on a couple of things. You’ve probably heard some alarming headlines about two potential complications. One involves the optic nerve and is called NAION. The other involves the stomach and is called gastroparesis.
The Eye Issue: NAION
Let’s start with the eye issue and explain what this actually is, because there’s been enough information floating around that I think it’s worth putting the concern into perspective. The condition is called nonarteritic anterior ischemic optic neuropathy, or NAION. It happens when blood flow to part of the optic nerve is interrupted. The optic nerve carries visual information from your eye to your brain, and NAION can produce sudden, painless vision loss, usually in one eye.
Most of the concern so far has centered on semaglutide, particularly in people with diabetes. I don’t want you to interpret that to mean this is necessarily a semaglutide-only issue, or that simply switching to tirzepatide or another medication means the concern goes away. Semaglutide is the drug for which we currently have the most data on this particular issue, and so far it has produced the clearest signal. There are also observational data involving GLP-1 medications more broadly, including semaglutide and tirzepatide. At this point, we don’t know whether this is specific to semaglutide, applies to some of these medications, or represents a class effect. We simply don’t have enough information yet to say.
There have been a number of observational studies, and remember, observational studies do not establish cause. They compare groups and look to see whether something happens more often in one group than another. If it does, we can identify an association. We cannot automatically say that one thing caused the other. So if NAION occurs more frequently among people taking semaglutide, that alone does not prove that semaglutide caused those cases.
Here’s what the numbers actually look like. A large meta-analysis of the observational data in people with diabetes found about 2.7 cases of NAION for every 10,000 people taking semaglutide for a year, compared with about 1.9 cases per 10,000 among those not taking semaglutide. So imagine 10,000 diabetic people taking semaglutide and perhaps two or three develop NAION. Then take another 10,000 similar diabetic people not taking it and perhaps one or two develop it. You see what I mean? This is exceedingly rare. There may be an increased risk, but we’re talking about a very small absolute number of events.
In people taking semaglutide for overweight or obesity without diabetes, an increased risk has not been clearly established. In that same meta-analysis, neither the observational weight-loss studies nor the randomized weight-loss trials showed a statistically significant increase in NAION. That probably pertains to many people reading this who are taking these medications primarily for weight loss. It doesn’t prove the risk is zero. It means we haven’t demonstrated an increased risk in that population.
There’s another complication when we try to figure out whether the medication is actually responsible. Diabetes, hypertension, smoking, obstructive sleep apnea, vascular disease, and certain optic nerve anatomy, particularly a crowded optic disc, already increase the risk of NAION. Many of the same people receiving these medications already have several of those risk factors. That makes separating the effect of the medication from the underlying patient much more difficult.
There’s also a good reason not to overstate the eye findings. A 2026 meta-analysis looked at 20 randomized clinical trials involving 83,288 people and found no statistically significant increase in ischemic optic neuropathy or other serious vision-threatening events with GLP-1 medications. That’s pretty reassuring. At the same time, these trials were not originally designed specifically to study NAION, and these events are extremely rare, so the results cannot rule out a small increase in risk. What they do tell us is that we’re certainly not seeing some large epidemic of serious optic nerve injury from these medications.
What About Gastroparesis?
Now let’s get into the next thing you’ll hear some people scream from the mountaintops about: gastroparesis.
Gastroparesis basically means that the stomach is not moving food through normally. Your stomach doesn’t just sit there like a bag holding food. The muscles in the stomach contract in a coordinated way, under the control of nerves, to grind food up and move it toward the small intestine. At the bottom of the stomach, the pylorus has to relax at the right time to allow that food to pass through. When that coordinated movement slows down substantially, food stays in the stomach much longer than it normally would. That’s when people can develop nausea, vomiting, early fullness, bloating, or the sensation that food is just sitting there.
Here’s what sometimes gets lost in this discussion: GLP-1 medications are supposed to slow gastric emptying. That’s part of what these drugs do. It contributes to why you feel full sooner and stay full longer. So if you’re taking one of these medications, some slowing of gastric emptying is expected. That does not mean something has gone wrong or that the medication has damaged your stomach.
Sometimes the effect becomes more pronounced than we want. Someone may start at too high a dose, increase the dose too quickly, or simply be particularly sensitive to the medication. Then you can see substantial nausea, early fullness, vomiting, or that feeling that food is just sitting in the stomach. That’s a recognized effect of these medications and one of the reasons we titrate them gradually rather than simply jumping to a high dose.
But that’s not really the controversy we’re talking about.
The claim that concerns people is that a GLP-1 can permanently paralyze your stomach, so that you stop the medication, the medication is gone, and you’re left with lifelong gastroparesis. That’s an entirely different claim from saying these medications slow gastric emptying while you’re taking them.
So what does the published evidence actually show? A recent systematic review found 12 published reports involving 13 patients with suspected GLP-1-associated gastroparesis. Here’s the part that’s important: 11 of those 13 patients had type 2 diabetes. Only two were non-diabetic patients using the medication for weight loss. Three of the diabetic patients already had evidence of pre-existing or subclinical gastroparesis before the GLP-1 was even started.
Most of these patients improved after the medication was discontinued, generally over days to weeks. In several cases where gastric-emptying studies were repeated, gastric emptying returned to normal. The two non-diabetic weight-loss patients also recovered rather than being left with permanent gastroparesis. One of them had complete resolution of her nausea at one-month follow-up after stopping semaglutide, and the other severe case resolved with supportive treatment.
The particularly prolonged and refractory case in that review was very different. That patient had diabetes and had already experienced recurrent episodes of diabetic gastroparesis before she ever received semaglutide. Her symptoms became substantially worse after starting the medication and persisted after it was stopped. But that’s precisely where causality becomes difficult. Diabetes itself can damage the autonomic nerves controlling the stomach and is a well-established cause of chronic gastroparesis. The authors of the review concluded that semaglutide most likely exacerbated her pre-existing diabetic gastroparesis rather than creating it from scratch.
That’s an important piece of context whenever you hear someone say, “I took a GLP-1, developed gastroparesis, stopped the medication, and it never went away.” If that person also has longstanding diabetes, you cannot automatically conclude that the GLP-1 permanently damaged the stomach. Diabetes itself may be responsible for the persistent disease.
Now, none of this proves that permanent GLP-1-induced gastroparesis could never happen. Medicine rarely gives us that kind of certainty. But based on the published evidence we currently have, we do not have convincing evidence that GLP-1 medications commonly cause permanent gastroparesis in people who previously had normal gastric function.
The Bottom Line
This is really more of a public service announcement than a normal SitRep. These medications have real physiologic effects, and like every medication, they can have real side effects.
There is a small observational association between semaglutide and NAION, particularly in people with diabetes, but whether the medication itself is causing those events remains uncertain. In people using semaglutide primarily for weight loss without diabetes, an increased NAION risk has not been clearly demonstrated.
As for the stomach, slowing gastric emptying is part of what GLP-1 medications are supposed to do. Sometimes that effect becomes excessive and causes significant symptoms, particularly when the dose is too much for that person or is escalated too quickly. That’s real, and it’s something we manage. But that’s very different from the claim that these medications routinely cause permanent, lifelong gastroparesis after the drug has been discontinued. We simply don’t have convincing evidence of that.
Based on the data we have right now, the average person taking a GLP-1 should not be walking around worried that he’s going to lose his vision or permanently damage his stomach.
Know about these things. Pay attention to symptoms. But keep the actual risk in perspective.
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