GLP-1 (Semaglutide, Tirzepatide, and Retatrutide)

Introduction

Just a few years ago, GLP-1 was discussed mainly in the context of treating type 2 diabetes. Today, it is increasingly associated with fat loss, because many people have noticed that these drugs can make weight reduction much easier. I have personally seen quite a few cases where losing weight - despite a well-structured diet and properly planned training - becomes so frustratingly slow that people start to lose hope before they see any real results from the effort they are putting in. In situations like that, Ozempic, Wegovy, Mounjaro, or other GLP-1-based medications can sometimes become a genuinely meaningful option when diet and training alone are no longer enough.

In practice, when people say "GLP-1," they are usually referring to one of three active compounds: semaglutide (Ozempic/Wegovy), tirzepatide (Mounjaro/Zepbound), or retatrutide (Triple G).

They are not identical, but they all share one key mechanism - GLP-1 signaling. That is what largely drives reduced appetite and better blood sugar control. Semaglutide works directly through that pathway, while tirzepatide and retatrutide add extra "switches" - GIP, and in the case of retatrutide, also the glucagon receptor - which may amplify the overall effect even further.

The topic has become so popular that it has even made its way into the satirical world of South Park.

What is GLP-1?

GLP-1 (glucagon-like peptide-1) is a natural gut hormone from the incretin family. It is released after a meal and helps the body maintain more stable blood glucose levels while promoting satiety sooner. The same pathway is used by GLP-1 receptor agonists (GLP-1 RAs), including semaglutide, tirzepatide, and retatrutide.

After eating, the intestines send signals to the pancreas and the brain that nutrients have entered the system. GLP-1 is one of the key signals in this process. As a result, the hormonal response after a meal is better matched to the actual amount of glucose present.

Main effects

Increases insulin secretion in a glucose-dependent manner. GLP-1 enhances insulin release when glucose levels are elevated. This is a glucose-dependent mechanism, which is why GLP-1 receptor agonists on their own are less likely to cause hypoglycemia than therapies that stimulate insulin release regardless of blood glucose levels. The risk increases mainly when they are combined with insulin or sulfonylureas.

Reduces post-meal glucagon levels. Glucagon promotes a rise in blood glucose, among other things by stimulating glucose production in the liver. After a meal, high glucagon levels are not beneficial. GLP-1 helps suppress it, which improves postprandial glycemic control.

Slows gastric emptying. GLP-1 slows the movement of food through the stomach, which leads to slower carbohydrate absorption and a more gradual rise in glucose. This effect supports satiety, but it also explains part of the gastrointestinal side effects, such as nausea, belching, a feeling of fullness, constipation, or diarrhea, especially when meals are large or very high in fat.

Affects appetite and satiety. GLP-1 acts on the centers involved in appetite regulation. For many people, this makes it easier to stop eating sooner and reduces the tendency to snack between meals. In practice, this means it becomes easier to maintain a calorie deficit without constantly fighting hunger.

Why these drugs last longer than natural GLP-1

Natural GLP-1 works only for a very short time because it is rapidly broken down by the DPP-4 enzyme. That is how it is meant to function physiologically - the hormone acts after a meal and then quickly disappears. GLP-1 receptor agonists are modified to resist this breakdown and keep the signal active much longer. This makes their effects on appetite and blood glucose more stable, rather than depending only on the short window after a meal.

In the context of fat loss, the key point is that the GLP-1 mechanism combines two major advantages in one - it helps reduce food intake while also improving post-meal glycemic control. That is largely why fat loss often becomes more predictable: it is easier to maintain a calorie deficit, and post-meal glucose fluctuations are less likely to trigger hunger spikes and energy crashes.

Semaglutide (Ozempic, Wegovy)

Semaglutide is a classic GLP-1 receptor agonist. In practice, it is essentially the same active compound - the main differences are the brand names and the indications it is most commonly prescribed for.

Semaglutide works by mimicking the action of the natural GLP-1 hormone, which reduces appetite and improves glycemic control after a meal. In real-world use, three effects tend to stand out most: reduced appetite, feeling satisfied sooner during meals, and less snacking between meals. At the same time, blood sugar control usually improves, especially after eating.

In clinical trials involving people with obesity, semaglutide at a dose of 2.4 mg once weekly produced an average weight reduction of about 15% over 68 weeks. The range of results is quite broad and depends on factors such as baseline body weight, dose tolerance, and consistency with diet and lifestyle changes.

In type 2 diabetes, the effect on body weight is often smaller than in people without diabetes, but the improvement in glycemic control is usually clear. Semaglutide also has supporting cardiovascular outcome data - first in people with type 2 diabetes (SUSTAIN-6), and later in people with obesity and established cardiovascular disease (SELECT).

Semaglutide dosing

Treatment starts with 0.25 mg once weekly for 4 weeks. The dose is then increased to 0.5 mg once weekly for the next 4 weeks.

If tolerance is good, the dose is increased further every 4 weeks: 1.0 mg, then 1.7 mg, then 2.4 mg once weekly, which is most commonly the target dose for weight loss.

In the treatment of type 2 diabetes, the target dose is often lower, commonly 0.5-1.0 mg once weekly, although some patients use 2.0 mg once weekly depending on glycemic control and tolerability.

If troublesome side effects occur, the usual approach is to stay on the current dose longer or return to the previous dose and increase more slowly.

Tirzepatide (Mounjaro, Zepbound)

Tirzepatide belongs to the same class of metabolic drugs as semaglutide, but its action is broader - it activates both the GLP-1 receptor and the GIP receptor. GLP-1 is responsible for a large part of the effect on satiety, gastric emptying, and post-meal glycemic control. The additional GIP signal strengthens the overall metabolic effect, which for many people translates into a more pronounced impact on body weight and blood sugar levels.

GIP (glucose-dependent insulinotropic polypeptide) is the second hormone in the incretin family. It is released after a meal and, like GLP-1, affects pancreatic function. Put simply, it helps the body respond more effectively to rising glucose after eating, and when combined with GLP-1 signaling, it may further enhance both the metabolic and weight-loss effect.

In clinical trials involving people with obesity or overweight, tirzepatide at doses of 10-15 mg once weekly produced an average weight reduction of around 20% over roughly 72 weeks. In type 2 diabetes, the improvement in glycemic control is usually very pronounced, while the reduction in body weight remains substantial, although on average it tends to be somewhat smaller than in people without diabetes.

Tirzepatide dosing

Treatment begins with 2.5 mg once weekly for 4 weeks. The dose is then increased to 5 mg once weekly.

If tolerability is good, the dose is further increased every 4 weeks: 7.5 mg, 10 mg, 12.5 mg, and 15 mg once weekly. For many people, the target dose is 10-15 mg, but in practice what matters most is tolerability and whether the effect remains stable over time.

If troublesome side effects occur, the usual approach is to stay on the current dose longer or return to the previous dose and increase more gradually.

In type 2 diabetes, especially during combination therapy - for example with insulin or sulfonylureas - dosing and the pace of dose escalation should be managed by a physician.

Retatrutide (Triple G)

Retatrutide is the most advanced of the drugs discussed here. At present, as of March 2026, retatrutide is in Phase 3 clinical trials, meaning it is at an advanced stage of efficacy and safety evaluation.

Retatrutide combines three mechanisms in a single molecule: it activates the GLP-1 receptor, the GIP receptor, and the glucagon receptor. GLP-1 remains the foundation, driving the effects on satiety, gastric emptying, and post-meal glycemic control. The GIP signal strengthens the metabolic effect, while glucagon receptor activation is intended to further enhance weight loss without worsening glycemic control.

Glucagon is a hormone that acts, in a sense, opposite to insulin - it raises blood glucose levels, among other things by stimulating the liver to release glucose. In retatrutide, glucagon receptor activation is meant to amplify the weight-loss effect, while the overall mechanism is balanced in a way that does not impair glycemic control.

In practical terms, retatrutide is designed to take the effects seen with earlier incretin-based drugs even further, especially in people with more severe obesity.

Clinical trials have shown very large reductions in body weight. At the highest doses used in studies, average weight loss exceeded 20%, and in some analyses reached about 24% after 48 weeks.

Retatrutide dosing

Retatrutide does not yet have an official dosing protocol for routine clinical use. At this stage, only the dosing schedules used in clinical trials can be described.

In studies, the drug was administered once weekly, with the dose increased gradually over time. Trial protocols included target doses of 1 mg, 4 mg, 8 mg, and 12 mg once weekly. The main differences were in the starting dose and the speed of dose escalation, with the goal of limiting side effects.

GLP-1 side effects and how to reduce them

The most common side effects of GLP-1 drugs are mainly related to slower gastric emptying and a stronger satiety signal. Symptoms usually become more noticeable after a dose increase and, in most cases, tend to ease over time.

Below are the most common side effects, along with practical ways to reduce or avoid them:

• Nausea - eat smaller portions, slow down when eating, and avoid packing too much fat into a single meal. After a dose increase, it often helps to stay longer at the same dose or raise it more gradually.
• Vomiting - this is most often seen after increasing the dose too quickly or after a large, heavy meal. Reducing the dose or slowing the escalation usually improves tolerability.
• Abdominal pain or upper stomach discomfort - smaller meals, less fat per meal, and eating without rushing usually help. If the symptom keeps coming back, consider a slower dose escalation.
• Belching, bloating, and a feeling of fullness - reduce meal size, limit very fatty foods, and eat dinner earlier. Try not to drink large amounts of fluid while eating.
• Reflux (heartburn) - smaller evening meals, finishing dinner earlier, and reducing fatty or spicy foods can help. Do not lie down right after eating.
• Constipation - increase fluid intake during the day, make sure your diet provides enough sodium and potassium, and increase fiber gradually, for example through vegetables or psyllium husk. A daily walk or other regular movement also helps.
• Diarrhea - for a few days, reduce the fat content of your meals, avoid alcohol, and check whether sweeteners may be contributing. Going back to smaller portions often helps as well.
• Fatigue - this is often related to a drop in overall calorie and fluid intake as appetite decreases. Make sure you are getting enough water, salt, regular small meals, and sufficient protein.
• Headache or a feeling of weakness - this is often linked to dehydration and low sodium intake. Increasing fluids and paying attention to electrolytes usually helps.
• Dizziness - this is typically made worse by too little food and too little fluid. Better hydration, electrolytes, and a slower pace of weight loss usually improve the situation.
• Injection site reactions (redness, itching) - rotate injection sites and avoid injecting into irritated skin.
• Hair loss - this can sometimes be seen during rapid weight loss, most often as temporary shedding or thinning. A slower rate of weight loss and adequate intake of protein and micronutrients usually help.

Two important practical points

When body weight drops too quickly, the risk of gallbladder-related problems, including gallstones, increases. This is not an issue unique to GLP-1 drugs - the same pattern is seen with any rapid and effective weight loss.

GLP-1 drugs should not be combined on your own with insulin or sulfonylureas without medical guidance, because this combination can increase the risk of hypoglycemia. On their own, GLP-1 drugs rarely cause hypoglycemia, but in combination therapy dose adjustments and glucose monitoring are often necessary.

The medical literature also describes rare but important gastrointestinal complications, such as pancreatitis, gastroparesis, or bowel obstruction. If severe, worsening abdominal pain or persistent vomiting develops, this should be treated as a reason for urgent medical evaluation.

In practice, tolerability usually improves when three things are combined: slower dose escalation, smaller meal portions, and proper fluid intake.

My Experience

My experience with GLP-1, specifically retatrutide (Triple G from Biolab), has been very positive so far. My wife started at 1 mg, and after two weeks we increased the dose to 2.5 mg, which is where we decided to stay. The effects were clearly noticeable and very much in line with what we expected. For a few days after moving up to 2.5 mg, she had mild nausea after larger meals. Interestingly, she still had the mental urge to eat from time to time, but physically her appetite was clearly lower, which made it much easier not to snack. Other than that, we did not notice any significant issues. Her body weight has been going down slowly, but steadily. Overall, she is happy with the results.