Ozempic, Wegovy, Mounjaro and Your Body: What Nobody Is Telling You About the Musculoskeletal Implications

GLP-1 medications are one of the most significant pharmacological developments in a generation. They are also being prescribed, discussed, and debated almost entirely without reference to what they do to your muscles, tendons, joints, and bones.

First: what is a peptide?

Before we get into Ozempic, it’s worth grounding the conversation in some basic biochemistry- because “peptide” has become a word that floats around wellness culture without much precision, and precision matters here.

A peptide is simply a short chain of amino acids, the same building blocks that make up proteins, but in a smaller, more targeted configuration. The body produces thousands of peptides naturally. They function as signalling molecules: hormones, neurotransmitters, growth factors, immune modulators. Insulin is a peptide. So is oxytocin. So is the hormone at the centre of this conversation; glucagon-like peptide-1, or GLP-1.

Synthetic peptides, including pharmaceutical-grade GLP-1 receptor agonists and the broader class of research and therapeutic peptides increasingly used in sports medicine, regenerative medicine, and metabolic health, work by mimicking or modulating these natural signalling pathways. They are not blunt instruments. They are highly specific, receptor-targeted molecules with effects that extend well beyond the system they were originally designed to target.

This specificity is both what makes them extraordinary and what makes the “just take Ozempic” conversation so incomplete.

The GLP-1 medications: a brief field guide

The class of medications colloquially referred to as “Ozempic drugs” are GLP-1 receptor agonists; synthetic peptides that bind to GLP-1 receptors in the pancreas, gut, brain, and increasingly, we’re discovering, throughout the body. They work primarily by stimulating insulin secretion in a glucose-dependent manner, suppressing glucagon, slowing gastric emptying, and via central nervous system action, significantly reducing appetite and food-seeking behaviour.

The case for GLP-1 medications: this is a genuine lever

Let’s be direct about what these medications do, because the reflex to dismiss them as a quick fix misses something important.

Obesity and metabolic dysfunction are not simply a failure of willpower operating against a neutral biological background. They involve dysregulated appetite signalling, insulin resistance, chronic low-grade inflammation, and neurobiological reward pathways that make sustained behaviour change extraordinarily difficult for many people. GLP-1 medications intervene directly at the level of that dysregulation. For people who have struggled with weight management despite genuine effort, they can be genuinely life-changing.

Clinically, they also provide a window; a period of reduced appetite, improving metabolic parameters, and often increasing energy, during which meaningful lifestyle change becomes substantially easier to establish. Think of it as a lever that lowers the gradient enough for the other work to gain traction. The reduction in joint load from significant weight loss is itself a musculoskeletal benefit; people with knee osteoarthritis, hip loading issues, and spinal compression who lose 10 to 15 percent of body weight can experience profound improvements in pain and function.

Used well, in the right patient, with appropriate medical supervision and a parallel lifestyle program, these medications can be a powerful catalyst. The problem is that “used well” requires more than a script and a weekly injection.

The musculoskeletal problem: what rapid weight loss does to your body composition

Here is what the obesity medicine conversation frequently glosses over, and what the physiotherapy conversation needs to say plainly.

Significant rapid weight loss without concurrent resistance training produces substantial muscle mass loss. The proportion varies by individual, rate of loss, dietary protein intake, and activity level — but studies on GLP-1-mediated weight loss consistently show that a meaningful percentage of total weight lost comes from lean mass rather than fat mass alone. One analysis of tirzepatide trial data found that lean mass accounted for approximately 25 to 40 percent of total weight lost, depending on the cohort and protocol.

From a musculoskeletal perspective, this matters enormously.

Muscle mass is not simply cosmetic. It is the primary driver of resting metabolic rate which means losing it makes weight regain more likely when the medication is ceased. It is the primary protector of joints under load, which means losing it increases compressive forces on cartilage, tendons, and subchondral bone during everyday activity. It is central to balance, fall prevention, bone density, and functional capacity across every domain of physical life. Sarcopenia, clinically significant muscle mass loss, is associated with increased fracture risk, reduced insulin sensitivity, and worse long-term metabolic outcomes. It is the opposite of what most people taking these medications are trying to achieve.

Tendon vulnerability

Beyond muscle, there is an emerging concern around tendon health in the context of rapid weight loss. Tendons adapt more slowly than muscle to changes in loading; their collagen remodelling cycle is measured in months, not weeks. When body weight drops rapidly, the mechanical loading environment that the tendon has adapted to changes faster than the tendon’s biology can respond. Combined with potential reductions in the anabolic hormonal milieu that accompanies significant caloric restriction, this creates a window of increased tendon vulnerability, particularly in weight-bearing tendons like the Achilles, patellar, and hip abductor tendons.

This is not a reason to avoid these medications. It is a reason to manage the transition carefully, with progressive loading rather than sudden increases in physical activity, and with physiotherapy input if tendon symptoms emerge.

Bone density

Emerging data, particularly from semaglutide trials, suggests modest reductions in bone mineral density associated with significant weight loss, likely mediated by reduced mechanical loading of bone as body weight falls. The clinical significance of this in otherwise healthy adults taking these medications for one to two years is not fully established, but it represents an additional argument for maintaining resistance training throughout the treatment period, given its well-established osteogenic effects.

GLP-1 medications as a tool within a broader system

The framing that does the most clinical harm is “I’m on Ozempic” as a complete sentence; a closed loop where the medication is the intervention and everything else is optional. The framing that produces the best long-term outcomes is quite different.

GLP-1 medications work best as a lever within a broader system that includes:

• Progressive resistance training — non-negotiable for muscle mass preservation. Two to three sessions per week minimum, with progressive overload. This is the single most important co-intervention and the one most frequently omitted from prescribing conversations.
• Adequate dietary protein — specifically targeted, not assumed. Most people on GLP-1 medications eat less without changing the macronutrient composition of what they eat, which means protein intake drops. It needs to be deliberately maintained.
• Mobility and movement variety — reduced appetite and increasing energy can be directed toward establishing movement habits that will outlast the medication. This is the window. Walking, clinical Pilates, swimming, whatever form of movement the person will actually sustain.
• A genuine shift in the rhythm — the medication can break a pattern of metabolic dysregulation and appetite dysregulation that has felt intractable. The goal is to use that break to establish new patterns of eating, moving, and recovering that don’t depend on the medication to be maintained.

The patients who do best long-term on GLP-1 medications are those who use the improved metabolic environment and reduced appetite as an on-ramp to a different life, not as a destination. The patients who struggle most are those who lose weight without building the physical capacity to maintain it — who emerge lighter but weaker, with no new habits and a metabolism that has further downregulated in response to the caloric restriction.

Beyond weight loss: the emerging research frontier

The story of GLP-1 medications is no longer primarily a weight loss story. The receptor systems these drugs engage are distributed throughout the body, in the cardiovascular system, the immune system, the brain, the reproductive system, and the research into non-metabolic applications is expanding rapidly. Three areas deserve specific mention.

MCAS: mast cell activation syndrome and GLP-1 receptor agonists

Mast Cell Activation Syndrome is a condition in which mast cells,  the immune system’s first-responder cells, release excessive chemical mediators, producing a wide range of allergy-like, multi-system symptoms including skin reactions, gastrointestinal dysfunction, fatigue, brain fog, and in severe cases, anaphylaxis. It is a condition that frequently goes undiagnosed for years, and for which treatment options have historically been limited to symptom management.

A 2025 retrospective case series published in The American Journal of the Medical Sciences (the first substantial clinical report on this application) examined 47 patients with difficult-to-treat MCAS who were given GLP-1 receptor agonist therapy, including semaglutide and tirzepatide. The outcome: 89 percent of patients experienced clinical benefit, often rapidly, within hours to days of the first dose, across inflammatory, neurological, gastrointestinal, and autonomic symptoms.

The proposed mechanism (we’re getting science-y here) involves GLP-1 receptor agonists reducing mast cell degranulation and modulating the NLRP3 inflammasome and NF-κB pathways, two core inflammatory control hubs. Tirzepatide’s dual GIP/GLP-1 agonism appears particularly relevant here, given its broader anti-inflammatory profile. Importantly, benefits were observed even in lean patients, suggesting the effect is immunological rather than purely mediated by weight loss.

This is early-stage evidence, a retrospective case series, not a randomised controlled trial, and low-dose or microdose protocols for MCAS are not yet standardised. But for a patient population that has often exhausted conventional options, it represents a genuinely significant signal. Relapse on discontinuation was common, which raises questions about long-term management strategy.

PCOS: polycystic ovarian syndrome and the GLP-1 connection

If you’re still with us on the science, we can layer up into women’s health! PCOS is the most common endocrine disorder in women of reproductive age, affecting an estimated 8 to 13 percent of women globally. It involves insulin resistance, androgen excess, ovulatory dysfunction, and metabolic dysregulation, a profile that maps closely onto the mechanisms GLP-1 receptor agonists target.

The evidence base for GLP-1 medications in PCOS is accumulating. A 2025 scoping review in Cureus covering semaglutide and tirzepatide in PCOS found improvements across weight, insulin resistance, menstrual regularity, hyperandrogenism markers, and pregnancy rates. Women with PCOS also show a distinct GLP-1 response pattern, with significantly lower incretin levels in the late phase of glucose tolerance testing compared to controls… identifying GLP-1 dysfunction as potentially integral to PCOS pathophysiology rather than simply comorbid with it.

From a musculoskeletal perspective, PCOS is relevant because it is associated with chronic low-grade inflammation, increased visceral adiposity, and the joint and tendon loading implications that accompany those metabolic features. The GLP-1 improvements in insulin sensitivity and inflammatory markers translate into a less inflammatory musculoskeletal environment, not a trivial benefit for a condition that affects women across their most physically active decades.

Endometriosis and peritoneal GLP-1: a new research frontier

Perhaps the most striking emerging finding in this space involves endometriosis, a condition affecting an estimated 190 million women worldwide, characterised by biologically active inflammatory tissue growing outside the uterus, and for which treatment options remain limited and frequently inadequate.

Still with me on the science? A peer-reviewed study published in the International Journal of Molecular Sciences (Krasnyi et al., 2022), subsequently referenced in a 2024/2025 review in Acta Obstetricia et Gynecologica Scandinavica, found that GLP-1 levels in the peritoneal fluid of women with endometriosis were significantly reduced compared to controls, with statistical significance at p = 0.009. This is the fluid that bathes the pelvic cavity, the same environment in which most endometriosis lesions develop.

The significance of this finding is considerable. Reduced GLP-1 in peritoneal fluid correlated with altered macrophage behaviour — specifically, reduced expression of the CD86 pro-inflammatory marker that plays a critical role in clearing endometrial cells that have migrated via retrograde menstruation. In other words, depleted peritoneal GLP-1 may impair the immune mechanism that normally limits endometriosis development. Proteases in the peritoneal fluid of endometriosis patients appear to degrade GLP-1 faster than in controls, creating a self-perpetuating pro-inflammatory environment.

No GLP-1 receptor agonist is approved for endometriosis. No Phase 3 clinical trial has been completed. This is emerging basic science, not clinical guidance. But it represents one of the most mechanistically compelling new research directions in endometriosis biology in years and it positions GLP-1 not merely as a metabolic drug but as a potential modulator of the peritoneal immune environment in which endometriosis operates.

For women navigating PCOS, endometriosis, or the overlap between metabolic dysfunction and reproductive health, these findings are worth understanding and worth discussing with a clinician who is tracking this literature.

The physiotherapy role in GLP-1 management

Physiotherapy is not a passive bystander in the GLP-1 conversation. If these medications are being used without a concurrent resistance training program and progressive loading strategy, the musculoskeletal risks; muscle mass loss, tendon vulnerability, bone density reduction are not being managed. That’s a gap physiotherapy fills directly.

At City Physio & Pilates, we work with patients who are on GLP-1 medications to establish and progress resistance and mobility programs that protect lean mass, support tendon and bone health through the weight loss phase, and build the physical capacity that makes the metabolic gains sustainable. Clinical Pilates is particularly well suited to this population; it provides progressive resistance loading in a controlled environment, with the joint-friendly properties that matter for people carrying significant load-related pain while their weight changes.

The medication is the lever. The rest of the system is where the outcome is actually determined.

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