GLP-1 receptor agonists represent one of the most significant advances in the management of type 2 diabetes and obesity in a generation. With the explosive growth of social media and direct-to-consumer advertising, these medications are now household names — yet the gap between public perception and safe clinical practice has never been wider.
What Are GLP-1 Receptor Agonists?
GLP-1 (glucagon-like peptide-1) is an incretin hormone secreted by L-cells in the small intestine in response to food intake. It stimulates insulin secretion in a glucose-dependent manner, suppresses glucagon, slows gastric emptying, and — critically — acts on hypothalamic satiety centres to reduce appetite and food intake. GLP-1 receptor agonists (GLP-1 RAs) mimic this action with a much longer half-life than the native hormone, making them suitable for once-weekly or even once-monthly dosing in newer formulations.
Currently available agents in Ireland and the United Kingdom include:
- Semaglutide — Ozempic® (0.5–2mg weekly injection, licensed for type 2 diabetes); Wegovy® (2.4mg weekly injection, licensed for obesity); Rybelsus® (oral, 7–14mg daily, licensed for T2DM)
- Liraglutide — Victoza® (daily injection, T2DM); Saxenda® (3mg daily injection, obesity)
- Dulaglutide — Trulicity® (weekly injection, T2DM)
- Exenatide — Byetta® (twice daily); Bydureon® (weekly)
- Tirzepatide — Mounjaro® — dual GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptor agonist, representing the next generation. Licensed for both T2DM and obesity in Ireland.
The Evidence Base
Cardiovascular Outcomes
The cardiovascular benefit of GLP-1 RAs is now among the best-documented in cardio-metabolic medicine.
- LEADER 2016 Liraglutide reduced major adverse cardiovascular events (MACE) by 13% versus placebo in patients with type 2 diabetes and high cardiovascular risk.
- SUSTAIN-6 2016 Semaglutide 0.5–1mg reduced MACE by 26% in T2DM patients with elevated cardiovascular risk — a landmark result.
- SELECT 2023 The most consequential trial in this space. Semaglutide 2.4mg (Wegovy) reduced MACE by 20% in patients with overweight or obesity and established cardiovascular disease — but without type 2 diabetes. This was transformative: GLP-1 RA cardiovascular benefit is independent of glucose lowering and extends to primary weight management indications.
- SURPASS-CVOT 2024 Tirzepatide demonstrated non-inferiority and numeric superiority to dulaglutide on MACE in T2DM; longer-term outcome data are awaited.
Weight Loss
- STEP-1 Semaglutide 2.4mg achieved mean 14.9% weight loss at 68 weeks in people with obesity without T2DM.
- SURMOUNT-1 Tirzepatide 15mg achieved mean 20.9% weight loss at 72 weeks in people with obesity — the highest pharmacological weight loss ever demonstrated in a placebo-controlled randomised trial.
- SURMOUNT-4 Weight regain after stopping tirzepatide was significant (+14% of body weight at 88 weeks), reinforcing that these are long-term, not short-term, treatments.
The SURMOUNT-4 data on weight regain is not a reason to avoid these medications — it is a reason to treat obesity as the chronic, relapsing metabolic disease it is, and to manage it long-term accordingly. Stopping a well-tolerated, effective medication for obesity is no different to stopping an antihypertensive.
Who Should Receive These Medications?
Current indications per NICE, EMA, and IPHA guidance:
- Type 2 diabetes: as add-on to metformin and other oral agents, or as first-line in combination with lifestyle modification when cardiovascular disease is present. GLP-1 RAs are preferred over sulphonylureas and DPP-4 inhibitors in patients with established CVD or high CV risk.
- Obesity: BMI ≥30 kg/m² with at least one weight-related comorbidity (T2DM, hypertension, dyslipidaemia, obstructive sleep apnoea, non-alcoholic fatty liver disease), or BMI ≥35 kg/m² regardless of comorbidities, as part of a structured specialist weight management programme.
- Cardiovascular risk reduction: Post-SELECT, semaglutide 2.4mg is indicated for reducing cardiovascular risk in patients with overweight or obesity and established atherosclerotic CVD, independently of glycaemic status.
Contraindications and Cautions
- Personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia type 2A or 2B (MEN2A/2B) — class contraindication. The biological basis is rodent data showing thyroid C-cell hyperplasia; human risk remains theoretical but is taken seriously as a regulatory requirement. A thyroid history and examination must precede prescription.
- Active or recent acute pancreatitis — do not initiate. History of pancreatitis is a relative contraindication requiring specialist risk assessment. Persistent epigastric pain radiating to the back during treatment must prompt urgent investigation and discontinuation.
- Severe gastroparesis — avoid; GLP-1 RAs further delay gastric emptying and may worsen symptoms significantly.
- Pregnancy and breastfeeding — contraindicated. Discontinue at least 2 months before planned conception (semaglutide) or 1 month (liraglutide). Women of childbearing potential should use effective contraception.
- Diabetic retinopathy with insulin therapy — an early worsening signal was observed in SUSTAIN-6. Subsequent analyses suggest this is related to rapid glucose normalisation rather than a drug-specific effect; however, ophthalmology review before initiation is prudent in patients with known proliferative retinopathy.
- Severe renal impairment (eGFR <15 ml/min) — avoid most agents in end-stage renal disease; semaglutide has emerging data in earlier CKD stages. Specialist renal-endocrine co-management is required.
Dose Titration — Why It Matters
Gastrointestinal side effects (nausea, vomiting, diarrhoea, constipation) are the most common treatment-limiting adverse effects and are dose-dependent. Slow, structured dose escalation substantially reduces their incidence and severity.
Semaglutide (Ozempic®): 0.25mg weekly for 4 weeks → 0.5mg for 4 weeks → 1mg maintenance → 2mg if needed in T2DM.
Semaglutide (Wegovy®): 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg; 4 weeks per step over 16 weeks total.
Tirzepatide (Mounjaro®): 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg; 4 weeks per step, up to 20 weeks escalation to maximum dose.
- Take the injection on the same day each week, at any time of day, with or without food
- Nausea is most common in the first 2–4 weeks after each dose increase — it will pass
- Eat smaller portions, chew slowly, avoid high-fat and spicy meals during the adjustment period
- Stay well hydrated — dehydration worsens nausea significantly
- If nausea is severe, delay dose escalation; do not discontinue. Contact your prescriber.
- GI symptoms indicate the medication is working — they reflect slowed gastric emptying, which drives satiety
The Muscle Loss Problem — What Media Coverage Ignores
Clinical trial data consistently shows that 25–40% of weight lost on GLP-1 receptor agonists can be lean mass (skeletal muscle), particularly in the absence of structured dietary protein and resistance exercise. This is not a GLP-1-specific problem — it occurs with all methods of caloric restriction at this magnitude — but it is insufficiently communicated in prescribing conversations and completely absent from social media promotion of these medications.
The consequences of significant lean mass loss include:
- Reduced resting metabolic rate, making long-term weight maintenance harder
- Increased risk of falls and functional decline, particularly in older patients
- Facial volume loss — the so-called "Ozempic face" — a consequence of subcutaneous fat and muscle loss, not an inevitable drug effect
- Sarcopenic obesity — a paradoxical and metabolically dangerous state
Every patient prescribed a GLP-1 receptor agonist for weight management should receive explicit guidance on:
- Protein intake: ≥1.2g/kg body weight/day; ≥1.5g/kg/day in adults over 65
- Resistance training: minimum 2 structured sessions per week targeting major muscle groups
- Dietitian involvement: particularly when significant weight loss (>10%) is the goal
The Serious Risks of Unregulated Use
GLP-1 receptor agonists are now available through unregulated online platforms, unqualified prescribers operating outside clinical governance frameworks, and compounding pharmacies. This has created a patient safety emergency.
- Counterfeit products: The US FDA, MHRA, and EMA issued multiple warnings from 2023 through 2025 regarding counterfeit semaglutide products of unknown concentration, purity, and sterility. Hospitalisations due to severe hypoglycaemia and anaphylaxis have been documented.
- Compounded semaglutide: During supply shortages, compounding pharmacies produced semaglutide variants (semaglutide sodium, semaglutide acetate) — chemically distinct from pharmaceutical semaglutide and with no clinical trial data supporting bioequivalence or safety.
- No baseline screening: Safe initiation requires HbA1c, renal function, thyroid history, pancreatitis history, BMI, cardiovascular risk assessment, and medication reconciliation. Online questionnaires do not substitute for clinical evaluation.
- Incorrect dosing: Without structured titration and medical supervision, severe GI effects, dangerous hypoglycaemia (particularly if the patient is concurrently on insulin or a sulphonylurea), and exacerbation of unidentified contraindications are real risks.
- No follow-up or monitoring: Structured follow-up identifies complications, assesses response, adjusts concomitant medications (particularly antihypertensives and diabetes agents as weight falls), and provides lifestyle support.
Adjusting Concomitant Medications
As weight falls and insulin sensitivity improves, patients on antihypertensives, diuretics, and insulin may require progressive dose reductions to avoid hypotension and hypoglycaemia. This is an active, clinical process that requires regular review — not a one-off prescription renewal. In our clinic, patients on GLP-1 RAs receive structured reviews at 4, 12, and 24 weeks, and 3–6 monthly thereafter.
When Specialist Review Is Needed
- Inadequate response (less than 5% weight loss) after 16 weeks at maximum tolerated dose
- Recurrent or severe hypoglycaemia on concomitant insulin or sulphonylurea
- Persistent abdominal pain — must exclude pancreatitis urgently
- Known or newly identified thyroid nodule or goitre — requires thyroid evaluation before initiation
- Weight loss plateau despite adherence — consider combination therapy, secondary obesity causes, or transition to bariatric surgery pathway
- Complex polypharmacy, CKD, or significant comorbidity requiring specialist co-ordination
GLP-1 receptor agonists are powerful, evidence-based medications with genuine cardiometabolic benefits. But their power demands clinical respect — proper patient selection, contraindication screening, structured titration, concomitant medication review, lifestyle support, and ongoing monitoring. They are not a quick fix, and they are not safe in unstructured, unmonitored settings.
Further Reading
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