TL;DR

GLP-1 medications — semaglutide, tirzepatide and the investigational retatrutide — mimic natural hormones and peptides in the gut and body to control blood sugar and appetite, driving meaningful weight loss for people with type 2 diabetes or obesity. They can also increase the risk of losing muscle alongside fat, which is why protein, resistance training, creatine and collagen deserve a place alongside your prescriber's care.

Welcome to a new era in metabolic health and weight management. GLP-1 medications have rapidly become a central topic in discussions about tackling conditions like type 2 diabetes and obesity. For many, these prescription drugs represent a significant shift, offering effective tools where previous approaches may have fallen short. With this rise in prominence comes a natural desire for clear, trustworthy information.

If you're researching, considering, or have recently started a GLP-1 medication, you're likely navigating new terminology, different brand names and important health considerations. You might be asking: what exactly are these medications, how do they differ, and — critically — how can you support your body effectively, especially when it comes to preserving muscle and optimising nutrition, while your weight changes significantly?

This guide from Youth & Earth sets out to give a balanced, authoritative overview of the GLP-1 landscape. We'll explain the different types of GLP-1 drugs, their reported benefits and drawbacks, and — just as importantly — practical, evidence-led guidance on nutritional support. The aim is to help you have informed conversations with your healthcare team, so your journey is as supported and well-rounded as possible.

GLP-1 Medications: What They Are and Why They Matter

GLP-1 stands for Glucagon-Like Peptide-1 — a natural hormone produced in your gut that helps regulate blood sugar, appetite and digestion. GLP-1 medications, known as GLP-1 receptor agonists, work by mimicking this hormone's action.

How do GLP-1 medications work? These effects don't happen in isolation — they cascade from the same hormonal signal, working together to change how your body processes food and regulates blood sugar:

• Stimulating insulin release: prompting the pancreas to release more insulin when blood sugar is high, helping to lower blood glucose.
• Suppressing glucagon release: reducing secretion of glucagon, another hormone that raises blood sugar, for better glycaemic control.
• Slowing gastric emptying: slowing how quickly food leaves the stomach, extending the feeling of fullness.
• Modulating appetite: acting on appetite-control areas of the brain, reducing hunger and increasing satiety.

Together, these four effects explain both the glycaemic control these medications were originally designed for, and the appetite suppression that has since made them so effective for weight management.

Initially developed for type 2 diabetes, the profound effects of GLP-1 medications on appetite and weight led to their approval for chronic weight management in many regions too. For people with obesity or type 2 diabetes, they represent a powerful tool for health improvements that diet and exercise alone may not have achieved.

The Current GLP-1 Market and What's Coming: Semaglutide vs Tirzepatide vs Retatrutide

The GLP-1 landscape is evolving quickly, with newer compounds targeting more incretins, metabolic gut hormones. Here's how the three you're most likely to hear about compare — the table below sets out the detail in full.

Semaglutide — the single GLP-1 receptor agonist

Semaglutide mimics the natural GLP-1 hormone directly, engaging its receptor to affect blood sugar, appetite and gastric emptying. It's sold as Ozempic (licensed for type 2 diabetes) and Wegovy (licensed for chronic weight management) — both approved in the UK. In large phase 3 trials, Wegovy produced substantial weight loss alongside reliable glycaemic control, and some studies point to cardiovascular benefits for people with type 2 diabetes. As with any significant weight loss, there's a risk of losing lean muscle mass alongside fat — one of the reasons the nutrition guidance later in this article matters.

Tirzepatide — going a step further with two receptors

Where semaglutide engages a single incretin pathway, tirzepatide engages two — acting as a dual GIP and GLP-1 receptor agonist. That combination has shown greater glycaemic control and weight loss than single-receptor agonists in head-to-head trials.[2] It's sold as Mounjaro (approved and licensed in the UK for type 2 diabetes) and, in the US only, as Zepbound for weight management. The same considerations apply as with semaglutide: cost and access can be factors, and rapid weight loss again carries a muscle-loss risk.

Retatrutide — a third pathway, still investigational

Retatrutide goes further still, engaging three receptors — GLP-1, GIP and glucagon. Early-phase trial data has suggested weight loss and metabolic improvements that may exceed those seen with dual agonists, but it's important to be clear: retatrutide is not yet licensed or approved for use in the UK or anywhere else.[1] It remains in clinical trials, and its long-term safety and efficacy are still being established.

What GLP-1 Medications Do to Appetite, Muscle and Nutrition

The primary way GLP-1 medications achieve their results — particularly in weight management — is through significant appetite suppression and slower gastric emptying. These effects are highly beneficial for reducing overall calorie intake, but they introduce a real challenge: making sure you still get enough nutrition.

When appetite drops sharply, it becomes harder to eat enough food — even nutrient-dense, healthy options. That can reduce protein intake specifically, and in any significant weight loss the body loses both fat and lean muscle. If protein intake is insufficient, or weight loss is very rapid, the share of that loss coming from muscle can be higher than it needs to be.

Preserving lean muscle matters for more than strength and physical function — muscle is metabolically active tissue, burning more calories at rest than fat does, so protecting it supports a healthier metabolism and better long-term weight-management outcomes. That's why GLP-1 medications, powerful as they are, call for a proactive, strategic approach to nutrition. Your prescriber or a registered dietitian can help you build a plan tailored to your circumstances.

The 5 Nutrition Priorities on a GLP-1

Here are five priorities worth raising with your prescriber or a nutritionist while you're on a GLP-1 medication:

Protein and Creatine for Muscle Preservation

As the section above sets out, preserving lean muscle mass is a cornerstone of healthy weight loss on a GLP-1. Rapid weight reduction can bring muscle loss alongside fat loss — which is where a targeted strategy of protein and, potentially, creatine becomes invaluable.[3]

Protein is the fundamental building block of muscle tissue. In a calorie deficit, your body may turn to muscle for energy if dietary protein is insufficient — so prioritising high-quality protein gives your body the amino acids it needs to repair and maintain muscle rather than break it down. Aim for a source of lean protein at every meal and snack: chicken, fish, eggs, Greek yoghurt, cottage cheese, legumes, or a high-quality protein powder all work well.

Creatine is one of the most well-researched supplements for supporting muscle strength and mass, and its benefits extend well beyond athletes to anyone looking to preserve muscle during calorie restriction. It helps regenerate ATP — the energy currency your cells rely on, especially during resistance training — which supports better performance in the gym. By enhancing your capacity for resistance exercise, it indirectly supports muscle preservation, helping you maintain strength and stimulate muscle protein synthesis even on fewer calories. It also draws water into muscle cells, contributing to muscle fullness.

Combined with regular resistance exercise, adequate protein and potentially creatine, you significantly improve your chances of preserving lean muscle mass on a GLP-1 medication. Always discuss adding creatine or any supplement with your prescriber first. For the full picture, see our dedicated guide: our creatine guide and, for a complete prioritised stack, our guide on how to prevent muscle loss on GLP-1s.

Collagen and Connective Tissue During Rapid Weight Loss

One common concern with significant, rapid weight loss is the impact on skin elasticity and connective tissue. As the body loses a large amount of fat, skin can struggle to retract fully, leading to concerns about loose or sagging skin.

Collagen is the most abundant protein in the body, forming a crucial part of skin, bones, muscles, tendons, ligaments and other connective tissue — providing structure, strength and elasticity. During rapid weight loss, demand on the body's own collagen synthesis can increase, and if nutritional intake isn't optimal, existing collagen structures may not be as well supported.

Supplementing with high-quality collagen peptides provides the amino-acid building blocks your body uses to synthesise new collagen. It isn't a magic fix for loose skin, but it can play a supportive role in skin health, elasticity and connective-tissue integrity as your body changes. For the full picture on why this matters specifically for GLP-1 users, see our dedicated article: Collagen on GLP-1 Medications.

Hair Loss on GLP-1s: Why It Happens and How to Limit It

Reports of hair loss can be distressing, and it's a common concern for people on GLP-1 medications. In most cases, though, this isn't a direct side effect of the medication itself — it's a temporary condition called telogen effluvium.[4]

Telogen effluvium happens when a significant physiological stressor — rapid weight loss, surgery, severe illness, or major dietary change — pushes a large number of hair follicles into their resting phase prematurely. Around two to three months later, those resting hairs shed, which is why many people notice hair loss a few months into their weight-loss journey.

With GLP-1s, the rapid weight reduction — combined with reduced calorie intake and the potential for specific nutrient shortfalls from appetite suppression — acts as that stressor. When the body isn't getting enough calories, protein or key micronutrients, it deprioritises "non-essential" functions like hair growth in favour of vital ones.

It's usually temporary, and growth typically resumes once the body adjusts and nutrition is restored. A few things help: keeping protein intake consistent (important for follicle health), paying attention to iron, zinc, biotin and vitamin D if dietary intake is limited (worth raising with your prescriber if a targeted supplement might help), working with your care team to keep the pace of weight loss manageable and well-nourished, and being gentle with hair care — avoiding harsh treatments, tight styles or excessive heat during this period. If hair loss is persistent or severe, it's worth speaking to your GP to rule out other causes.

The Thyroid Connection: Caloric Restriction and Hair Health

While telogen effluvium explains most shedding, there is another factor to consider: changes in thyroid activity. When taking GLP-1s, profound appetite suppression can sometimes lead to excessive caloric restriction, which forces the body into a protective, energy-conserving state that directly impacts how your thyroid functions.

The thyroid gland acts as your metabolic thermostat, but it is incredibly sensitive to starvation signals. If your daily food intake drops too drastically for too long, your system adapts by lowering its conversion of active thyroid hormone (T3). This slows your basal metabolic rate to preserve energy — a brilliant survival mechanism, though frustrating for weight loss and hair health.

Because hair follicles contain some of the fastest-dividing cells in the body, they rely on a constant, robust supply of active thyroid hormones to function. When T3 levels drop due to severe under-eating, the hair growth cycle stalls. New growth slows down, existing strands may become dry and brittle, and overall shedding increases.

Like telogen effluvium, this diet-induced thyroid shift is temporary and reversible. The most effective fix is ensuring your calorie deficit remains moderate rather than extreme. Collaborating with your care team to find a sustainable calorie target keeps your metabolism — and your hair follicles — running smoothly. If your hair loss is accompanied by intense fatigue, feeling constantly cold, or very dry skin, it is worth asking your GP for a routine thyroid blood test to ensure your levels remain stable.

Women's Health and GLP-1s: PCOS, Endometriosis and What to Know

The metabolic and hormonal effects of GLP-1 medications extend beyond blood sugar and weight, with emerging relevance in some women's health conditions.

PCOS (Polycystic Ovary Syndrome)

PCOS is a complex hormonal condition affecting millions of women, often marked by insulin resistance, hormonal imbalances such as elevated androgens, irregular periods and sometimes weight gain. Because the insulin resistance seen in PCOS resembles a pre-diabetic state, GLP-1 medications have become a compelling area of investigation — improving insulin sensitivity and supporting weight loss, both central to managing PCOS symptoms, and potentially helping reduce androgen levels and regulate cycles.[5] GLP-1s aren't specifically licensed for PCOS in the UK; where they're used, it's off-label, at a prescriber's discretion, typically alongside an approved indication like type 2 diabetes or obesity.

Endometriosis

Endometriosis — where tissue similar to the womb lining grows outside it, causing pain and inflammation — has a less direct link to GLP-1s, though some research points to a connection between endometriosis, inflammation and metabolic factors. Any potential benefit here would work through anti-inflammatory or metabolic pathways rather than a direct mechanism, and the evidence is much earlier-stage. GLP-1s are not licensed or routinely used for endometriosis; any use would be highly investigational and solely at a specialist prescriber's discretion.

Female-specific considerations during weight loss

Whatever the underlying condition, women on GLP-1 medications losing significant weight should keep a few things in mind: bone health (rapid weight loss can affect bone density, so adequate calcium, vitamin D and weight-bearing exercise matter), hormonal fluctuations (significant body changes can affect menstrual cycles), and muscle preservation — prioritising protein and resistance training just as anyone would, but with particular relevance for strength, metabolism and vitality.

For more on why creatine and resistance training matter specifically for women, see our guide: creatine for women.

If you're considering a GLP-1 for PCOS, endometriosis or any other women's health concern, an in-depth conversation with your gynaecologist, endocrinologist or GP is essential — they can give tailored advice based on your individual profile and the latest evidence.

Youth & Earth Collagen GLP-1 Formula: What It Is and Who It's For

At Youth & Earth, we know that optimising metabolic health means working in harmony with your body's natural pathways — which is why we developed our Collagen GLP-1 Formula, designed to natively stimulate appetite-regulating hormones and balance blood sugar. It serves as an advanced natural approach for anyone looking to proactively support their metabolic journey or maintain healthy weight management.

The formula is built on a synergy of cutting-edge ingredients chosen to optimise glucose control and sustain natural fullness. Nextida®, a groundbreaking active biopeptide platform, goes far beyond traditional structural collagen; it is clinically proven to stimulate your gut's native GLP-1 secretion, flattening post-meal blood sugar spikes by an average of 42%. Solnul™, a prebiotic resistant starch, feeds the microbiome to encourage digestive comfort while actively prompting the deep, lower-intestinal release of native satiety signals. Finally, Eriomin®, a patented citrus flavonoid blend, provides targeted metabolic support by assisting insulin sensitivity and clinically boosting the body's own baseline GLP-1 levels to smooth out daily energy crashes.

The formula is designed for anyone seeking a natural, proactive approach to blood sugar stability, metabolic efficiency, and appetite management — whether as a standalone wellness strategy or to preserve healthy metabolic rhythms. It's intended as premium nutritional support to work alongside your body's natural chemistry within a broader health plan, including a balanced diet and regular exercise, under the guidance of your healthcare professional.

The Collagen GLP-1 Formula is launching soon — join the waitlist below to be first to know when it's available, with pricing and subscription details to follow at launch.

How to Get Started Safely (With Your Prescriber)

Starting a GLP-1 medication is a significant step towards better health. To make sure that journey is safe, effective and well-supported, the most important thing you can do is keep an open, ongoing dialogue with your healthcare team.

Before starting
Have a thorough conversation with your GP or specialist prescriber about your full medical history, current medications, potential side effects, and how a GLP-1 fits your overall health goals — and make sure you understand the specific medication prescribed (semaglutide, tirzepatide, or otherwise), its dosage and what to expect.

While on a GLP-1 medication
Attend all scheduled follow-up appointments — these are vital for monitoring progress, adjusting dosage and addressing concerns. Report any side effects, even mild ones, rather than waiting for them to resolve on their own. Work with a registered dietitian or nutritionist who understands GLP-1s to build a personalised meal plan that covers protein, micronutrients and fibre despite a reduced appetite, and talk to your GP or a qualified fitness professional about incorporating resistance exercise, which is key for muscle preservation. And before adding any new supplement — protein powder, creatine or collagen included — check with your prescriber or pharmacist first, to make sure it's appropriate for you and won't interact with your medication.

Your health journey is unique, and partnering closely with your healthcare professionals is what lets you get the most from a GLP-1 medication while protecting your nutritional status and overall wellbeing.

Coming soon: the Youth & Earth Collagen GLP-1 Formula

Our Collagen GLP-1 Formula is designed to sit alongside your prescriber's care, and it's launching soon. Join the waitlist below and we'll be first to let you know the moment it's available — by email, and by text too if you'd like.

Whatever stage you're at, the best next step is the same one: bring these nutrition priorities to your next appointment and build the plan together.

Frequently Asked Questions

What's the difference between Ozempic and Mounjaro?

Ozempic is semaglutide and engages a single hormone receptor (GLP-1); Mounjaro is tirzepatide and engages two (GLP-1 and GIP). Tirzepatide has shown somewhat greater average weight loss and glycaemic control in trials, though individual response varies, and both are licensed in the UK specifically for type 2 diabetes rather than weight loss.

What is retatrutide?

Retatrutide is a newer compound that engages three hormone receptors — GLP-1, GIP and glucagon — rather than one or two. It's shown promising results in early trials, but it is not yet licensed or approved anywhere, including the UK; it remains investigational.

Which GLP-1 causes the most muscle loss?

There's no reliable data ranking the three specifically by muscle loss. What the evidence does show is that faster, larger overall weight loss — which tirzepatide and retatrutide can produce more of — tends to carry a greater muscle-loss risk than slower loss, regardless of which medication is driving it. That makes the nutrition priorities in this guide relevant whichever GLP-1 you're on.

What supplements should I take on a GLP-1?

Discuss any addition with your prescriber first, but the priorities most people should ask about are protein (to preserve muscle), creatine (to support strength and training capacity), collagen (for skin and connective tissue), and covering micronutrient gaps like iron, zinc and vitamin D if your appetite has dropped significantly.

Does a GLP-1 cause muscle loss?

Not directly — but the rapid weight loss GLP-1s can produce means the body loses both fat and lean muscle, and if protein intake or resistance training aren't prioritised, the muscle share of that loss can be higher than it needs to be. It's manageable with the right nutrition approach rather than something to be alarmed by.

Does a GLP-1 cause hair loss?

Usually not directly. Hair shedding reported on GLP-1s is typically telogen effluvium — a temporary reaction to the physiological stress of rapid weight loss and reduced calorie or protein intake, not the medication itself. Additionally, excess caloric restriction can signal your thyroid to lower its conversion of active hormone (T3) to conserve energy. Because hair follicles require massive cellular energy to grow, this temporary metabolic slowdown can stall their cycle. Both forms of shedding are reversible and tend to resolve as nutrition, calorie intake, and weight stabilise.

Can you take a GLP-1 for PCOS or endometriosis?

For PCOS, GLP-1s are sometimes prescribed off-label where insulin resistance is a factor, at a prescriber's discretion. For endometriosis, the evidence is much earlier-stage and use would be highly investigational. Neither is a licensed indication in the UK, so this is a conversation to have directly with a specialist.

Should I take collagen on a GLP-1?

It can be highly beneficial. Traditional collagen peptides supply the amino acids needed to support skin elasticity and connective tissue during weight loss. Targeted biopeptides like Nextida® go beyond basic structural building blocks to actively stimulate your body's native GLP-1 pathways, helping to optimise glucose control and sustain natural fullness alongside your treatment. Read more: Collagen on GLP-1 Medications.

Is creatine safe on GLP-1 medications?

Creatine has a well-established safety profile in the general population, but as with any supplement alongside a prescription medication, confirm with your prescriber first. Many people use it specifically to help preserve strength and muscle mass during GLP-1-driven weight loss — see our full guide for more: our creatine guide.

References

[1] Aronne LJ, Horn DB, le Roux CW, Ho W, Falcon BL, Gomez Valderas E, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity. N Engl J Med. 2025;393(1):26-36. DOI: https://doi.org/10.1056/NEJMoa2416394

[2] Jastreboff AM, Kaplan LM, Frías JP, Wu Q, Du Y, Gurbuz S, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526. DOI: https://doi.org/10.1056/NEJMoa2301972

[3] Li S, Zhang Y, Li M, et al. Effect of glucagon-like peptide-1 receptor agonists and co-agonists on body composition: Systematic review and network meta-analysis. Metabolism. 2025;164:156113. DOI: https://doi.org/10.1016/j.metabol.2024.156113

[4] Eisa N, Barood S, et al. Lean Mass Changes With Incretin Therapy Versus Lifestyle Intervention: A Systematic Review and Meta-Analysis of Randomised Controlled Trials. Diabetes Obes Metab. 2026;28(6):4818-4827. DOI: https://doi.org/10.1111/dom.70666

[5] Jensterle M, et al. GLP-1 receptor agonist treatment in women with polycystic ovary syndrome-a systematic review and meta-analysis. Eur J Endocrinol. 2026;194(3):25-39. DOI: https://doi.org/10.1093/ejendo/lvag033