GLP-1 Medications — What They Actually Do, What the Data Shows, and What Nobody Is Telling You

YOUR HEALTH — Issue No. 11

The mechanism, the benefits, the risks, and the real conversation happening in the exam room.

Let's start with the elephant in the room.

GLP-1 therapy carries a stigma that is worth addressing directly before anything else.

The criticism goes something like this: "These medications disincentivize a healthy lifestyle. People should just eat better and exercise more."

It is a fair point — in theory. The easiest way to lose weight is to never put it on in the first place. A lifetime of good nutrition and consistent exercise is the right answer. Nobody disputes that.

But that is not the reality sitting across from me in the exam room.

The reality is a person who looked up one day and found themselves 75, 100, or 150 pounds overweight. Who has spent years — sometimes decades — eating and living a certain way. Whose brain, habits, and relationship with food have been shaped by stress, circumstance, and time. Asking that person to simply eat less and move more — without any help — has an extremely high failure rate. Not because they lack willpower. Because changing an entire behavioral profile built over years is genuinely hard, and the biological deck is stacked against them.

Obesity is a health crisis. We can acknowledge that and offer real help — or we can withhold it on principle and watch people struggle.

I am in the camp of helping people.

GLP-1 medications are not a shortcut. They are not for everyone. They have real side effects and real limitations. But they are the most effective medication available for weight loss — and they stabilize the number one driver of obesity: overeating. You lose weight on these medications because you simply are not eating as much. That is the mechanism. That is the honest answer.

Here is how I actually use them in practice.

My first goal is to decrease appetite and get the patient a win. A real, visible, encouraging win. Once that happens — and it usually does — I shift the conversation. Now we talk about protein intake. Eating schedules. Food choices that support what the medication is starting. This is where the behavioral work begins — not as a prerequisite to treatment, but as a natural progression once the patient has momentum and confidence.

After those habits start forming, I bring in movement. Step counts. Resistance training. An exercise plan that fits their life — not an idealized version of it.

GLP-1 therapy is not the complete answer. But it gives people a genuine chance to reverse decisions that accumulated over years and work toward a better quality of life.

My goal — and what I tell every patient — is that the endgame is forming new habits. New ways of eating, moving, and living that eventually make the medication less necessary. When that happens — when I see those habits taking hold — that is when I start the conversation about discontinuation.

That is the honest version of this. That is Plain Medicine.

How GLP-1 medications actually work

GLP-1 stands for glucagon-like peptide-1 — a hormone your body naturally produces in the gut after eating. It signals the brain that you are full, slows the rate at which food leaves your stomach, and stimulates insulin release in response to elevated blood sugar.

GLP-1 medications mimic and amplify this natural hormone — staying active in the body far longer than the GLP-1 your body produces on its own. The result is sustained appetite suppression, slower gastric emptying, and reduced food intake throughout the day.

The glucose-dependent mechanism — and why it matters:

One of the most important and least discussed aspects of GLP-1 medications is that their effect on insulin is glucose-dependent. In plain terms — they only stimulate insulin release when your blood sugar is actually elevated. When glucose is normal, the medication has little to no effect on insulin secretion.

This is fundamentally different from older diabetes medications like sulfonylureas — which stimulate insulin regardless of your blood sugar level and can cause dangerous low blood sugar. GLP-1 medications carry a much lower risk of hypoglycemia as a result.

One important exception: patients taking a GLP-1 alongside a sulfonylurea have a higher risk of low blood sugar because the sulfonylurea's effect is not glucose-dependent. If you are on both, your provider should be monitoring closely and may reduce your sulfonylurea dose.

Why side effects happen:

The most common side effects of GLP-1 medications — nausea, vomiting, constipation, and reduced appetite — are a direct consequence of the mechanism. Slowing gastric emptying means food sits in the stomach longer. That is why nausea is most common when starting the medication or increasing the dose, and why most patients find it improves significantly after the first few weeks as the body adjusts.

Starting at the lowest dose and titrating up slowly is the standard approach — and for good reason. Patience with the dose escalation schedule reduces side effects significantly.

Why some people lose more weight than others

This is one of the most common questions in the exam room — and the honest answer is more nuanced than most people expect.

GLP-1 medications work by reducing how much you eat. That is the primary mechanism of weight loss — not a separate fat-burning effect. This means the amount of weight you lose is directly related to how much your caloric intake actually decreases.

I regularly have patients tell me they "don't really eat that much" — and then lose 30 pounds on a GLP-1. That tells me their actual intake before starting was higher than they realized. Most people significantly underestimate how much they consume. These medications often reveal that gap rather than create some separate metabolic effect.

The behavioral piece — stress eating and emotional hunger:

GLP-1 medications reduce physical hunger effectively. What they do not always address is the psychological relationship with food — stress eating, emotional eating, and habitual eating patterns that exist independent of physical hunger signals.

A patient who eats primarily in response to stress, boredom, or emotion may find that the medication reduces their appetite but does not fully address the underlying trigger. This is one reason outcomes vary — and one reason behavioral support alongside medication produces better long-term results than medication alone.

Individual biological variation:

Beyond behavior, genuine individual variation exists in GLP-1 receptor sensitivity, medication tolerance, and dose response. Some patients achieve significant weight loss at lower doses. Others require maximum doses to see meaningful results. Some experience significant side effects that limit dose escalation. These differences are real and not fully predictable.

Beyond weight loss — what the data actually shows

GLP-1 medications were developed for diabetes. What researchers discovered along the way is that their effects extend far beyond blood sugar and weight. Here is what the strongest evidence currently supports:

Cardiovascular disease — FDA approved for semaglutide:
In 2024, the FDA approved semaglutide (Ozempic/Wegovy) specifically to reduce cardiovascular events in overweight and obese adults — the first time a weight loss medication received this indication. The SELECT trial showed approximately a 20% reduction in major cardiovascular events including heart attack and stroke. Tirzepatide (Mounjaro/Zepbound) has demonstrated cardiovascular protection in clinical trials as well — a formal FDA cardiovascular indication is anticipated but not yet approved as of this writing.

Chronic kidney disease — FDA approved for semaglutide:
In January 2025, the FDA approved semaglutide for chronic kidney disease in patients with Type 2 diabetes. Clinical trials demonstrated meaningful reductions in kidney disease progression. Tirzepatide has also shown promising kidney data in high-risk CKD subgroups — additional indications are expected as trial data matures.

Obstructive sleep apnea — FDA approved for tirzepatide:
In 2024, the FDA approved Zepbound (tirzepatide) as the first medication ever approved for moderate-to-severe obstructive sleep apnea in adults with obesity — a landmark approval for a condition that previously had no medication-based treatment option. Clinical trials showed meaningful reductions in breathing disruptions during sleep.

Heart failure with preserved ejection fraction (HFpEF):
The STEP-HFpEF trial demonstrated that semaglutide improved symptoms, exercise capacity, and quality of life in patients with obesity-related HFpEF — one of the most difficult-to-treat forms of heart failure. This is a meaningful development for a condition with limited effective treatment options.

A note on the ACP's new guidance:
Just this month, the American College of Physicians released new guidance on obesity treatment — joining the World Health Organization, The Obesity Society, and the Obesity Medicine Association in formally supporting GLP-1 and GLP-1/GIP medications as the appropriate next step when lifestyle modifications alone do not achieve adequate results. This represents a significant shift in how the medical establishment views obesity treatment.

Conditions under active research:*

Early studies are also showing promise in depression, multiple sclerosis, Parkinson's disease, and inflammatory conditions like psoriasis — suggesting that GLP-1 medications may have broader anti-inflammatory and neuroprotective effects that go well beyond their original indication.

These are not current treatment indications. They reflect an emerging body of research — not established clinical guidance.

What happens if you stop — the rebound reality

This is the question most patients ask after they start seeing results. And it deserves an honest answer.

Studies consistently show that discontinuing GLP-1 therapy leads to significant weight regain. A real-world study of semaglutide found that patients who stopped the medication regained approximately two-thirds of their lost weight within six months. The STEP 4 and SURMOUNT 4 trials — randomized withdrawal studies — confirmed this pattern: discontinuation is consistently followed by rapid weight regain and a reversal of cardiometabolic benefits.

Approximately 46.5% of patients stop taking GLP-1 medications within one year — often due to cost, side effects, or the belief that they no longer need the medication after losing weight. For many, weight returns quickly after stopping.

This is not a character flaw. It reflects the biology of obesity — a chronic condition that, like hypertension or diabetes, often requires ongoing treatment to maintain results.

Is this a forever medication?

For many patients — honestly, yes. Just as blood pressure medication controls blood pressure only while you take it, GLP-1 medications control appetite and weight only while they are active in your system. Stopping removes that effect.

However — and this is the goal I discuss with every patient — if the period on medication is used intentionally to build new habits, reduce portion sizes, establish an exercise routine, and change the relationship with food, some patients are able to maintain meaningful weight loss after discontinuation. It requires significant behavioral change during the medication period. It is possible. It is not guaranteed.

What about muscle loss?

This is one of the most important — and most underreported — aspects of GLP-1 therapy.

Approximately 25-40% of the weight lost on GLP-1 medications comes from lean body mass, not fat. For someone losing 40 pounds, that may mean 10-16 pounds of muscle. For older adults already at risk of age-related muscle loss — a condition called sarcopenic obesity — this is a meaningful clinical concern.

The good news: this is largely preventable.

The STEP-UP trial substudy showed that patients over 65 who performed resistance training during GLP-1 therapy retained 85% of their lean mass — compared to only 55% in sedentary patients over 65. Adding resistance training to GLP-1 therapy cuts lean mass loss roughly in half.

For anyone on GLP-1 therapy — especially adults over 60:

It is also worth noting that similar or greater lean mass loss occurs with very-low-calorie diets and bariatric surgery. GLP-1 medications are not uniquely muscle-wasting — but the concern is real and warrants proactive management.

The Member deep-dive this week covers tapering strategies for discontinuation — what the early data shows about slowly reducing dose to minimize rebound, what is and is not yet proven, upcoming GLP-1 therapies in the pipeline including oral agents and next-generation dual and triple agonists, the maintenance dose conversation, and a plain English breakdown of what Mounjaro and Zepbound do differently than Ozempic and Wegovy.

Next week: Alpha-gal syndrome — the tick bite that can make you allergic to red meat. A condition affecting hundreds of thousands of Americans — most of whom do not know they have it.

Plain Medicine is published for educational purposes only and does not constitute medical advice or establish a patient-provider relationship. Always consult your healthcare provider before making medical decisions.

— Kyle