MythBusting GLP-1s: TRUTH About Weight Loss Medications

Today, we’re diving into one of the most talked-about topics in health and weight loss right now: GLP-1 medications like semaglutide and the newer dual GIP/GLP-1s like tirzepatide. You’ve probably seen the headlines, scrolled past a few TikToks, or heard a friend mention it — but with all that noise comes a lot of confusion, half-truths, and flat-out myths.

Today we’re breaking it all down. What’s real? What’s hype? And what do you actually need to know if you’re using these medications — or thinking about it? Let’s separate science from scare tactics and get to the truth, one myth at a time.

Myth #1: GLP-1s Cause Dangerous Muscle Loss

The claim:  “GLP-1s cause massive muscle loss.”

Truth:
This is an overstatement.

Some loss of lean mass is normal with any kind of weight loss — whether it’s through diet, medication, or surgery. What studies show is that with medications like semaglutide (Wegovy) and tirzepatide (Zepbound), about 20–25% of the total weight lost comes from lean mass, and the rest is fat — which is exactly what we’re targeting in obesity treatment. That 20–25% figure isn’t unique to these meds; it’s actually pretty typical in weight loss without focused resistance training or optimized protein intake.

You may also hear “You’ll lose all your muscle and become frail on GLP-1s.”

Truth:
You won’t “lose all your muscle.” In fact, muscle loss is preventable by maintaining adequate protein intake, resistance training, and managing weight loss pace. Furthermore, many patients gain strength and mobility as excess weight comes off.

And lastly, my favorite myth is “You can’t preserve muscle on GLP-1s.”

Truth:
That’s completely false — muscle loss isn’t inevitable on GLP-1s if you take the right approach. You can absolutely preserve muscle by making a few intentional choices: aim for enough protein each day (a good goal is around 0.8 grams per pound of body weight), include some strength or resistance training a couple times a week, and avoid losing weight too quickly. These simple steps go a long way in protecting your lean mass while still getting all the benefits of weight loss.

One study on semaglutide showed that people lost an average of about 15% of their body weight, and only around 3–4% of that was lean mass. So if someone drops 30 pounds, maybe 6 to 8 of those pounds might be lean mass—not ideal, but definitely not disastrous either, and very manageable with the right lifestyle habits. 

The truth is, while some lean mass loss is expected with any type of weight loss, research shows that most of the weight lost on GLP-1s is actually fat, not muscle. For example, in the STEP 1 trial, about 80% of the weight lost on semaglutide came from fat, and only about 20% from lean tissue (as we mentioned earlier). 

The SURMOUNT-1 trial with tirzepatide showed similar results—significant fat loss with relatively preserved muscle, especially when paired with resistance training. And that’s important, because preserving muscle during weight loss helps protect metabolism, strength, and overall health. With good nutrition and movement, GLP-1s can lead to healthier body composition—not just a lower number on the scale.

Okay, moving along to the next myth …

Myth #2: GLP-1s Can Cause Blindness

The truth: This myth stems from concerns about diabetic retinopathy worsening, which is tied to how quickly blood sugar drops, not to the drug itself.

In the SUSTAIN-6 trial (Marso et al., NEJM, 2016), a small subset of patients with pre-existing advanced diabetic retinopathy saw transient worsening—but only in those with rapid improvements in A1c.

No increased rates of blindness or new-onset retinopathy have been found in non-diabetic patients using GLP-1s for weight loss.

The bottom line is that those without advanced diabetic eye disease, there’s no increased risk of blindness. Patients with diabetic retinopathy should be monitored closely—but this is about glycemic management, not a direct effect of the medication.

Myth #3: GLP-1s Cause Kidney or Liver Damage

The truth: This is false. In fact, GLP-1 agonists may protect kidney and liver function—especially in patients with diabetes or fatty liver disease.

The most recent notable study showing kidney‑protective effects of a GLP‑1 receptor agonist is the FLOW trial, which evaluated semaglutide in people with type 2 diabetes and chronic kidney disease (CKD). This double‑blind, randomized, placebo‑controlled trial included 3,533 participants followed for a median of 3.4 years and found that semaglutide reduced the risk of major kidney‑related events—including kidney failure, substantial eGFR decline, and death from renal or cardiovascular causes—by 24% compared to placebo.

A 2025 meta-analysis of multiple randomized controlled trials (11 studies, 85,373 participants) concluded that GLP‑1 receptor agonists reduced the risk of composite kidney failure outcomes by 18%, kidney failure by 16%, and all‑cause death by 12%.

And let’s not forget the SMART trial, involving obese patients with kidney disease but without diabetes, found that semaglutide protected kidney function in this non‑diabetic, CKD‑affected population. 

When it comes to the liver, there’s actually growing evidence they’re actually helping reverse non-alcoholic fatty liver disease (NAFLD).

The STEP 1 MRI substudy and SURPASS-3 MRI substudy have shown people on these medications can reduce liver fat by 30 to even 50% and in some cases, completely resolve liver inflammation — that more serious form called NASH, where fat is combined with inflammation and early scarring.

The LEAN trial found that nearly 60% of people taking semaglutide had resolution of NASH, without worsening their liver scarring. That’s huge.

And even better, we’re seeing these effects even in people who don’t have diabetes. Just losing weight helps fatty liver, but these meds seem to do more than that — they actually target inflammation and fat storage in the liver itself..

The bottom line is GLP-1s are not nephrotoxic or hepatotoxic. In fact, they may be organ-protective—especially for people with underlying metabolic issues.

Myth #4: These Drugs Lead to Bone Loss

The claim: “You’ll get osteoporosis from losing too much weight!”

The truth: While extreme weight loss can affect bone density, GLP-1s themselves do not cause bone loss, and may even have neutral or protective effects on bone.

A 2022 study in Bone found no significant change in BMD (bone mineral density) in adults treated with semaglutide for obesity. While the SUSTAIN and PIONEER programs found no increased risk of fractures in semaglutide-treated patients versus placebo.

Truly, concerns about bone loss are more relevant in extreme calorie restriction or eating disorders—not evidence-based GLP-1 treatment with appropriate nutrition.

Myth #5: Everyone Gets Gastroparesis

The claim: “These medications paralyze your stomach”

The truth: GLP-1s slow gastric emptying, which is part of how they work—making you feel full longer. But this is dose-dependent and typically reversible.

A 2023 FDA safety review found that true gastroparesis is extremely rare and resolves when the drug is stopped.

Reality check: Nausea, early satiety, and mild bloating are common but manageable side effects. True, lasting gastroparesis is not typical, especially when doses are titrated gradually.

Myth #6: GLP-1s Make Your Hair Fall Out

The claim: “You’ll lose a ton of hair—just like with crash diets”

The truth: Hair shedding is not directly caused by GLP-1 medications. Instead, it’s often a temporary, non-scarring condition called telogen effluvium, which can happen with any rapid weight loss, regardless of the method.

A 2023 analysis from the American Academy of Dermatology emphasized that telogen effluvium is common with surgical or medical weight loss, especially if patients lose more than 10% of their body weight within a few months.

In clinical trials like STEP and SURMOUNT, hair loss was not listed as a common side effect, but patient-reported data show it occurs occasionally—likely tied to nutritional stress, not the drug itself.

So why does hair loss happen? We’ve talked about this before, but I don’t want to leave this important information out. 

Hair follicles are sensitive to internal stress. Rapid changes in caloric intake, nutrient levels (like iron, zinc, and biotin), or hormone balance can push hairs into the shedding phase. This is a delayed effect, often showing up 2–3 months after weight loss begins, and it typically resolves within 6–12 months.

What helps is slower, sustained weight loss, prioritizing protein intake, supplementing iron, zinc, and biotin if deficient, and avoiding very low-calorie diets and over-restriction.

Myth #6: GLP-1s Cause Dehydration

It’s a common myth that GLP-1 medications cause dehydration — but that’s not exactly true. The medication itself doesn’t directly dehydrate you. What can happen is that some people experience nausea, vomiting, or a reduced appetite early on, which can lead to drinking less water without realizing it. That’s where the dehydration risk comes in.

A good general rule for staying hydrated is to aim for half your body weight in ounces of water per day. So, for example, if you weigh 160 pounds, try to drink around 80 ounces daily — more if you’re active or live in a hot climate.

Electrolytes can also be really helpful, especially if you’re feeling tired, dizzy, or crampy. I like LMNT packets — they’re a clean option with no sugar and a good balance of sodium, magnesium, and potassium. The sodium in LMNT packets helps keep you hydrated by pulling water into your cells and helping your body retain the fluids it needs to function properly. Just one a day can make a big difference in how you feel.

Myth #7: You Have to Stay on GLP-1s Forever or You’ll Gain All the Weight Back

The claim: “As soon as you stop taking it, all the weight comes back”

The truth: Yes—some weight regain is likely after stopping GLP-1 medications. But that doesn’t mean they’re ineffective or that you’re doomed to rebound completely. The same pattern happens after any type of weight loss intervention, whether it’s a diet, surgery, or medication.

The STEP 4 trial (Wilding et al., 2022) showed that participants who stopped semaglutide after 20 weeks regained an average of 6% of their weight loss over the next year. But it’s important to note that they still weighed less than at baseline—and many continued to experience improvements in blood pressure, cholesterol, and insulin sensitivity.

Similarly, in SURMOUNT-4, patients who stopped tirzepatide also regained weight, but less than they lost.

So why does this weight gain happen?

I feel like the answer to this is obvious, but I’ve found that it’s not. 

GLP-1s change your appetite and hunger cues. Once the medication is stopped, your body’s baseline hunger signals return—and often with increased intensity, due to metabolic adaptation. But this isn’t unique to GLP-1s. The same thing happens after crash diets, keto, intermittent fasting, or bariatric surgery if long-term changes aren’t made.

The real issue isn’t the drug—it’s the lack of a plan after the drug. To help make results sustainable, we need to use the medication as a tool, not a crutch. We should use it to help us lose weight and understand our hunger cues, while transitioning to a whole foods, protein based diet coupled with resistance training to help preserve and build muscle. 

Just remember, if you’re coming off a GLP-1 and want to keep the momentum going, the key is to approach it thoughtfully. Tapering slowly under medical supervision can help your body adjust and reduce the chances of weight regain. At the same time, this is a great moment to double down on the habits that helped you feel your best while on the medication. Think ongoing support—like working with a health coach, joining a support group, or even doing behavioral therapy—to help reinforce those long-term lifestyle changes. It’s not just about what you stop; it’s about what you keep doing that matters most.

You don’t necessarily have to stay on GLP-1s forever—but if you stop without a plan, some weight regain is very likely. Think of them like glasses: they help you see clearly while you build the habits to eventually navigate without them. For some, that may mean staying on a lower maintenance dose long-term—just like with blood pressure or cholesterol meds.

What are my final thoughts?

I want to be clear—GLP-1s aren’t magic. But they are powerful tools when paired with education, support, and smart lifestyle changes. 

Myths like ‘you’ll go blind,’ ‘you’ll lose all your hair,’ or ‘you’ll be stuck on these meds forever’ aren’t just misleading and downright false—they discourage people from getting real help. 

So if you’re thinking about these medications, get informed, ask the hard questions, and make your decision based on science—not fear.

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Until next time, be well, and as always, have a happy, healthy week.