From appetite-suppressing drugs to new triple-action molecules: what they really are, what they promise, and what they're teaching us about human metabolism
To understand why these drugs changed medicine, you have to start with something that numbers don't tell.
Imagine a hunger that never goes away. Not the normal hunger, the kind that comes before lunch and passes after eating. A deep, constant hunger, present even right after meals. A noise that doesn't quiet down. For many people, it's been like this for years: they can never feel truly full, truly content. When they eat something, a part of their mind is already thinking about the next bite. When they're out, they can't fully enjoy the moment because in the background, there's always that craving, that desire. It's not even always true hunger: sometimes it's the need to eat when stressed, sad, angry, lonely; food as a release valve, followed by guilt.
These people start at a disadvantage when they try to lose weight. For them, a diet doesn't just mean eating less: it means amplifying that noise until it becomes deafening. Hunger becomes stronger, impairs concentration, disrupts sleep, and occupies the mind. It's almost impossible to endure for long. Not because they lack willpower, but because they are fighting against their own brain's biology.
GLP-1 receptor agonist medications have done something for many of these people that no diet has been able to do: they have turned down the volume. For the first time in years, the background noise quieted down. Finally full, finally able to get up from the table without thinking about it, finally free to live without that constant thought.
This is the starting point, but to understand how they achieve this, and why they are much more than simple “hunger suppressors,” one must understand what GLP-1 really is.
What is GLP-1
GLP-1 (Glucagon-like peptide-1is not a foreign substance: it is a hormone that our body produces naturally, especially in the intestine, in response to food. It is part of the continuous dialogue between the gut and brain that regulates hunger, satiety, and sugar metabolism.
The drugs in this class (the best known is semaglutide or also known as Ozempic, Wegovy) are enhanced, long-acting versions of this hormone. They work because GLP-1 receptors are strategically distributed throughout the body:
- in brain, especially in the centers that regulate appetite and satiety (but also in those of nausea, which explains a common side effect);
- in the’intestine, where they slow down stomach emptying, prolonging the feeling of fullness;
- in Heart and blood vessels, where they exert protective effects;
- along the’Gut-brain axis, modulating food-related reward signals.
The main effect, therefore, isn't “burning” something: it's reducing the drive to eat. More satiety, slower gastric emptying, and a decreased reward response to food stimuli through dopamine pathways. In other words: the drug lowers that background noise we were talking about.
The three generations: “eat less,” “manage better,” “burn more.”
The most interesting thing about this class of drugs is that it has evolved over generations, and each generation isn't simply more potent: it acts on different biology. The logic boils down to three signals.
First generation GLP-1 only: “eat less”. Semaglutide acts on a single target: the GLP-1 receptor. In clinical trials, it produces weight loss of around 15-16%, a result that is already unprecedented for a drug.
Second-generation GLP-1 + GIP: “manage nutrients better.”. The tirzepatide (Mounjaro, Zepbound) adds a second target, GIP, another incretin hormone. GIP appears to improve insulin sensitivity and directly influence adipose tissue metabolism, guiding nutrient utilization. The result is not just “greater appetite suppression”: weight loss approaches or exceeds that of 20%, and there are indications that GIP may mitigate some of the loss of muscle mass and improve the metabolic flexibility of fat cells. Many patients also report better tolerance for the same amount of weight loss.
Third-generation GLP-1 + GIP + glucagon: “burns more”. The Retatrutide (still experimental, not approved) adds a third target: glucagon. And this represents a change in metabolic state, not just in potency. Glucagon promotes lipolysis (the breakdown/mobilization of fat) and increases energy expenditure by acting on the liver, adipose tissue, and the nervous system. In Phase 2 trials, weight loss approached 24–25%, with a slightly greater effect in women.
This is an important point, however: the effect of glucagon on raising basal metabolism requires relatively high doses, likely from 5 mg upwards, not simple microdosing. It's not an effect that “turns on” at minimal doses.
And pay attention to the terminology, because there's a lot of confusion out there: there are no “GLP-2” and “GLP-3” as second- and third-generation weight-loss drugs. There really is a hormone called GLP-2, but it does something else entirely (it regulates gut growth). What we call second and third generation are actually molecules that target more receptors simultaneouslyGLP-1 alone, then GLP-1 + GIP, then GLP-1 + GIP + glucagon. This is precisely the key concept: the more targets you hit, the more the effect grows and changes nature.
Glucagon, however, comes with a cost: it can increase heart rate and add cardiovascular stress. Some (anecdotal) reports mention a higher resting heart rate and reduced heart rate variability, both generally considered unfavorable, even though the long-term clinical consequences remain unknown.
Beyond Weight: An Inquiry into Metabolism
This is where the story gets really interesting, because these drugs are turning out to be much more than weight-loss tools. They seem to act on a healthier metabolic state In general, the benefits that emerge in very different fields seem to follow more from this than from weight loss alone.
Brain. The signs regarding prevention are promising. Large observational studies of people with diabetes link the use of GLP-1 to a lower incidence of dementia: a cohort of about 110,000 people found a risk reduction of approximately 10%, while analyses of even larger registries reported even greater reductions. The problem is that these are observational studies, and much of the benefit could simply stem from weight loss and a reduction in visceral fat. In terms of mechanisms, GLP-1 activates a protein called AMPK (a cellular “energy sensor”), reduces inflammation, appears to improve the clearance of debris by microglia, and shifts the processing of the amyloid precursor protein toward a less harmful pathway.
But honesty is needed, and here comes the data that changes the picture: at the end of 2025, the first major dedicated phase 3 trial, called EVOKE, on about 3,800 people with early-stage Alzheimer's, It has not reached its goal. Semaglutide did not slow down the already established disease. Therefore, the correct distinction is this: GLP-1 couldto play a role in prevention in metabolically at-risk populations (an interesting signal, but observational and unproven) while as cure Despite the presence of Alzheimer's, the study conducted specifically for it was negative.
Heart. Here, however, the evidence from controlled trials is solid and consistent: a real cardiovascular benefit. Part of this comes from weight loss (less visceral fat, lower blood pressure, improved blood sugar), but there are also weight-independent mechanisms: GLP-1 receptors in the heart and blood vessels, improved endothelial function, less vascular inflammation, more available nitric oxide, and a better lipid profile.
Joints. GLP-1s appear to improve hip and knee osteoarthritis. And not just due to mechanical “offloading” from lower weight: a 2026 study in Cell Metabolism, designed specifically to isolate the effect from weight loss (by controlling diet), has shown that semaglutide acts directly on cartilage cells. Through the same AMPK axis seen in the brain context, it reprograms chondrocyte metabolism, from glycolysis to mitochondrial oxidative phosphorylation, which is much more energy-efficient, promoting cartilage restoration. A small pilot study in humans seems to confirm this.
It's the common thread throughout the entire story: whether we're talking about Alzheimer's, osteoarthritis, or obesity, the benefits seem to stem from a healthier cellular metabolism, not just from losing weight.
Side effects and the great misunderstanding
This is probably the most important part, because there is a huge confusion between what is actually caused by the drug and what is instead caused by how it is used.
Let's start with the side effects very, those directly related to GLP-1. They are primarily gastrointestinal: nausea, vomiting, diarrhea, constipation, and a feeling of early fullness—a direct consequence of slowed gastric emptying and central appetite suppression. These side effects can be quite severe: more than 50% of people prescribed a GLP-1 for obesity discontinue treatment within a year. Other drug-related effects include worsening of pre-existing gastroparesis and, rarely, pancreatitis.
And then there's everything else: hair loss, sagging skin, loss of muscle mass, fatigue, low hormones, which is commonly attributed to GLP-1, but with GLP-1 It has almost nothing to do with it.
Let's do a thought experiment. Take a healthy, fit twenty-year-old. Have them eat very little for six months, not enough protein, no micronutrients, low energy, and also remove training. What happens? They lose fat, of course. But they also lose muscle mass, bone density, hair; their skin loses tone because the body lacks the energy and building blocks to regenerate collagen and tissues. It's not toxicity: it's malnutrition. And it would happen with or without medication.
The point is that without a GLP-1, these people would almost never be able to maintain such rhythms because their bodies would scream with hunger. The drug silences that hunger, and this allows some to push themselves into such an aggressive deficit that they effectively inflict the same damage as prolonged malnutrition, often worsened by the mistaken belief that “the higher the dose, the less I eat, the faster I lose weight.” It's the same mechanism as contestants on certain extreme weight loss TV shows, who regained everything afterward: it wasn't the “method,” it was a crash diet taken to the extreme.
So, a large part of these side effects are not due to GLP-1, but to a poorly set diet, which would produce the same catastrophic results anyway. The solution is not to demonize the drug, but to use it well: adequate protein, resistance training, a reasonable deficit.
It is also worth distinguishing two other often misunderstood cases:
- The gallstones are related to weight loss Fast in itself (this also happens after bariatric surgery), not due to a specific medication toxicity.
- The deteriorations of retinopathy observed in some cases seem to be linked to rapid glycemic changes, which can precipitate retinopathy already existing, not a direct damage from the drug to the eye.
And the thyroid cancer, which we keep hearing about? The signal comes from rodents (a specific type of tumor), and it forms the basis for a precautionary warning. But in humans, the most recent and extensive studies, involving over 100,000 people, do not show a clear increase in risk. True caution is only for those with a personal or family history of medullary thyroid carcinoma or related genetic syndromes.
A note on muscle, and on retatrutide
There is a lot of enthusiasm about the idea that retatrutide “spares muscle” and leads to almost exclusively fat loss. It must be stated clearly: controlled studies do not confirm it. The best available data suggest a loss of lean body mass in proportions similar to those of other GLP-1 agonists (up to 25–40% of the weight lost may be non-fat tissue, a significant finding for older adults and those at risk of sarcopenia).
Where does the idea of “muscle-sparing” come from then? From two sources: an ambiguous phrase in a published article (with wording perhaps influenced by the manufacturing company), and anecdotes from the fitness and bodybuilding communities, which report loss of almost only fat. One concrete and rarely declared possibility weighs on the latter: the use of anabolic substances.
That said, some of the “lean mass loss” measured is not functional muscle, but non-contractile tissue (intramuscular fat, water). And where the loss exceeds that observed with diet and lifestyle alone, the explanation may lie in population differences: those who use these drugs tend, on average, to be more sedentary, eat worse, and train less.
There is also a fascinating hypothesis, yet to be proven, to explain why lean, metabolically healthy people seem to respond differently: a hormone produced by the liver, the’FGF21, capable of significantly increasing energy expenditure and perhaps protecting muscle. People with obesity often show “FGF21 resistance,” similar to insulin resistance. The idea, I emphasize: a hypothesis, is that in lean individuals, retatrutide can better engage these pathways that increase metabolism and preserve muscle, while in obesity, they are muted. Fascinating, but we are in the realm of theories to be verified.
The practical message, however, is simple: during weight loss with these medications, adequate protein and resistance training are not optional; they are what determine how much of the lost weight is fat and how much is muscle.
Addictions: The Same Reward System
One of the most surprising effects emerges from the fact that GLP-1 acts on the dopaminergic reward circuits, the same ones that govern not only appetite but also addiction. Hence the growing interest. But the evidence forms a gradient, and it's worth respecting:
- Alcohol: is the most studied area. A Phase 2 trial from 2025 showed reduced consumption and craving; however, a meta-analysis of the few available randomized studies is still inconclusive. Promising, not proven.
- Smoke / nicotineSignal present in some subgroups, not yet established.
- Other substances (cocaine, opioids): almost only data on animals, for now.
- Behavioral dependencies (games, pornography, and the like): there is practically nothing about man here: it's an extrapolation from the mechanism, a plausible theory rather than data.
In summary: the idea that GLP-1 “acts on the common engine of addictions” is biologically sensible and truly interesting, but it ranges from alcohol, where we are starting to have concrete data, to behavioral addictions, where for now there is only theoretical promise.
And the mood? An open question
If the same reward circuits also govern pleasure, motivation, and emotional bonding, it's natural to wonder: can long-term use of a drug that modulates them flatten emotions, love, passion, and joy?
It's a legitimate and fascinating question. But the evidence, today, largely points in this direction opposite to what one might fear. The key study shows that semaglutide reduces appetite increasing the dopaminergic reward signal, and, unlike drugs that flatten the dopaminergic tone indiscriminately, it seems preserve general sensitivity to pleasure, dampening only the excessive response to food and substance stimuli. Several reviews even suggest that these medications may relieve anhedonia, especially in depression linked to insulin resistance.
That said, the picture is genuinely two-sided: a minority of people report emotional blunting and apathy, and there have been signs (later downplayed as not causal) of negative mood and thoughts. It should also be said that large obesity trials excluded those with a history of depression, so robust data is lacking.
The honest phrasing, then, is this: it's an open question. For most people, the effect on mood seems neutral or favorable; a minority reports flattening; and science does not yet have a definitive answer. No alarmism, no promises.
What happens when you quit
It's the most frequent question, and the one with the most misunderstandings: “as soon as you stop, you gain all the weight back, so you're condemned to use them for life.”.
Let's set things straight. It's true that, in studies, most people regain a lot of the weight after stopping. But this It's not the medication that harms you nor does it “break” your metabolism. It's the exact same phenomenon that causes crash diets to fail: when you lose weight, the body defends its set point, The weight your body is used to, with two mechanisms that don't depend on willpower. Energy expenditure drops, and hunger hormones go wild: ghrelin rises, leptin falls, hunger increases. And these changes persist for a long timea classic study showed that, one year after weight loss, hormones that drive weight regain had not yet returned to baseline levels, in people without no eating disorder. The body fights to regain lost fat regardless of how “clean” you eat.
So the precise wording is: GLP-1 does not Cause the recovery, but not cure obesity, the Check As long as you take it. You stop taking it, and the underlying biology returns. Just like a blood pressure or cholesterol medication: you stop, and the values go back up. Not because the medication damaged you, but because the underlying condition wasn't cured, just kept in check.
But there is good news, and it's important: The set point is adjustable. It is not a life sentence. Obesity medicine today agrees that it can be lowered, but weight loss is necessary gradually and then maintain The new weight for months, giving the body time to accept it. Crash diets fail precisely because they skip this phase. There is a large registry of over ten thousand people who have lost significant weight and kept it off for years. without medication, the proof that it can be done. It must be said, for honesty's sake, that they succeed with continuous effort (a lot of physical activity, constant attention): “lowering the set point” doesn't usually mean “now I can eat freely and not worry about it anymore,” but rather “the new weight becomes defensible with effort." sustainable instead of extreme”.
In this context, the correct way to use these medications becomes clear: as a Help, not as a permanent crutch. You reach the goal, then gradually reduce the dose by increasing calories towards maintenance, you “reignite” what the deficit had shut down (thyroid, hormones, muscle mass), you return to a state of energetic abundance, you shift your focus to recovery and calm instead of restriction. It's hard, it takes time and discipline, and the medication doesn't do it for you, but with a GLP-1, the journey is more manageable because hunger remains under control while the body readjusts.
And for some people, especially those with more severe obesity, where biology is more stubborn, a low, long-term maintenance dose remains the right choice. And it is a choice legitimate, not a failure. Regaining weight after stopping is not a moral failing: it's biology. Which path is right for each person, whether to come off it entirely or remain on maintenance, is an individual decision to be made with your doctor.
In summary
GLP-1 receptor agonists, and new dual and triple action molecules, are much more than appetite suppressants. For those who have lived for years with that constant “noise” of hunger, they have achieved something no diet ever could. And as we study them, they are revealing unexpected biology: concerning the brain, heart, and joints, which seems to revolve less around lost weight and more around a healthier metabolic state.
But they are neither magic nor a shortcut. They work best as a tool within a strategy: protein, training, a reasonable deficit, and a plan for what comes after, rather than as a passive solution. They are prescription medications that require medical supervision: dosage, duration, withdrawal, and management of effects must be overseen by a professional, never improvised.
Perhaps the biggest lesson is precisely this: these drugs are proving to be less of tools for weight loss, and more of probe Within human metabolism, which shows us how much of us is still to be understood.
What do you think?
Tell me yours in the comments, I'm reading!
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It's important to open a new window on human physiology. There's no miracle drug, and sometimes willpower alone isn't enough. Together, maybe they'll hit the jackpot! Biology matters much more than we've thought for years. My NO STRESS theory, which is almost impossible in this society, is to exercise and move whenever you're feeling overwhelmed, and eat well with local products.
Very balanced article. I believe the most important message is precisely this: these drugs do not replace a healthy lifestyle, but they allow many people to finally do what was previously almost impossible, because they reduce that constant hunger which is often mistaken for a lack of willpower.
At the same time, it's crucial to remember that they are not a shortcut: proper nutrition, strength training, and medical supervision remain essential to achieve lasting benefits and limit side effects. It will be interesting to see what long-term studies tell us, especially regarding metabolic effects beyond simple weight loss.
Good evening Oliver, congratulations on the article. I am a pharmacist and I liked the quality of the presentation. .
From a scientific point of view, I'm happy to share Dr. Lettieri's observations.