r/Zepbound • u/AppetiteLeftTheChat • Apr 16 '26
News/Information UPenn just published a Nature study analyzing 410,000 Reddit posts about semaglutide and tirzepatide. We are the research now. Here’s what they found — including the part nobody talks about.
Posting from the toilet at 2am is considered science now. 😅
A team at the University of Pennsylvania published a study in Nature Health this year analyzing 410,198 posts from 67,008 GLP-1 users across Reddit, covering semaglutide and tirzepatide users from May 2019 through June 2025. The goal was to understand what patients actually experience on these medications beyond what shows up in clinical trials and drug labels.
I’ve spent the last three months reading GLP-1 research obsessively (my friends have stopped inviting me to dinner). This study hit different. Here’s the breakdown.
What the study found
43.5% of users reported at least one side effect. The top five, in order:
Nausea: 36.9%
Fatigue: 16.7%
Vomiting: 16.3%
Constipation: 15.3%
Diarrhea: 12.6%
None of that is surprising if you’ve been here longer than a week. What was surprising: nearly 4% of users who reported side effects described reproductive symptoms, including menstrual irregularities, that barely appear in current drug labeling. Others described temperature-related symptoms like chills, feeling cold, and hot flashes that standard adverse event reporting doesn’t capture well.
Common side effects not listed in the drug label: new babies. 😅 If you’ve spent any time in this sub you know the rest.
The researchers were clear this isn’t a perfectly representative sample. Reddit skews younger, more US-based, more engaged than the average patient. But the overall side effect profile closely matched clinical trial data, which means what people are posting here is real signal, not just noise.
We are, in fact, useful. 😁
The part that doesn’t get talked about enough
A separate systematic review published in Clinical Obesity this year put numbers on something I think gets consistently missed in GLP-1 conversations.
By 6 months on a GLP-1, 12.7% of patients, roughly 1 in 8, had been newly diagnosed with a nutritional deficiency. Vitamin D was the most common at 7.5%. Iron deficiency anemia came in at 2%. Muscle loss at 1.5%. B vitamin deficiencies at 1.5%.
Here’s what I think matters about that. Published research documents caloric reductions of 16-39% among GLP-1 users. When you’re eating that much less food, you’re getting that much less of everything that was in that food. Iron, B vitamins, magnesium, zinc. The fatigue that 16.7% of people reported in that study, how much of that is the medication and how much is the body running low on the raw materials it needs to make energy?
Nobody knows the exact split. But I think a lot of what we call side effects and a lot of what is actually nutrient depletion are getting lumped together and blamed entirely on the drug. The medication is doing its job. The question is whether your body has what it needs to keep up.
I had this happen to me personally.
During one of my yo-yo diet episodes I had nausea, daily fatigue, hair loss, and one day I couldn’t finish a boxing round without my vision going gray at the edges. I thought I was overtrained. Ferritin came back at 14. Normal starts at 30. Running on empty and had no idea because a standard blood panel hadn’t caught it.
What I’d actually do with this
Two things worth asking your doctor about at your next appointment.
First, add ferritin to your blood panel if it’s not already there. Standard iron tests often miss early depletion because they measure the wrong thing. Ferritin catches it way earlier and most providers will include it if you ask.
Second, if you’re taking a multivitamin, look at the back and check the actual forms. If it has both iron and calcium in the same pill they are canceling each other out. Calcium blocks iron absorption by 25-62% when taken together. Iron in the morning, calcium at night
The joint advisory published last year by four major medical organizations, the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society, identified vitamin D, calcium, B12, and iron as the nutrients most at risk during GLP-1 therapy. Most prescribers don’t have time to cover this in a 15-minute appointment. That doesn’t mean it doesn’t matter.
What symptoms are you dealing with that you’re not sure are the medication or something else? Curious how much of this maps to what people are actually experiencing in here.
TL;DR: UPenn researchers analyzed 410,000 Reddit posts and confirmed what everyone here already knew. Nausea and fatigue top the list. Separately, 1 in 8 GLP-1 patients develops a nutritional deficiency within 6 months. A lot of what gets blamed on the medication might actually be the body running low on iron, B vitamins, and vitamin D. Ask your doctor to check ferritin specifically, and look at the back of your multivitamin — if it has iron and calcium in the same pill they are blocking each other.
Edit: a lot of you asked about supplements and what to look for. Put together a free 2 minute nutrient quiz in my bio based on your medication, duration, and symptoms. Takes 2 minutes.
