What GLP-1 RAs Are — and Are Not

GLP-1 receptor agonists mimic the endogenous incretin hormone glucagon-like peptide 1, stimulating glucose-dependent insulin secretion, suppressing glucagon, slowing gastric emptying, and producing central satiety signals. In clinical trials, semaglutide 2.4 mg (Wegovy) produced mean body weight reduction of 14.9% at 68 weeks (STEP-1; Wilding et al., NEJM 2021), while tirzepatide demonstrated up to 22.5% weight loss in the SURMOUNT-1 trial (Jastreboff et al., NEJM 2022).

These are powerful, injectable prescription medications classified as controlled therapeutic agents by the HPRA (Ireland) and MHRA (UK). They are not nutritional supplements, lifestyle aids, or cosmetic treatments. Their use must be embedded within structured clinical management.

Established Contraindications and Safety Signals

All GLP-1 RAs carry a black-box warning from the FDA and class warning from the EMA regarding thyroid C-cell tumours observed in rodent studies. Although causality in humans has not been definitively established, prescribers are required to screen for:

  • Personal or family history of medullary thyroid carcinoma (MTC)
  • Multiple Endocrine Neoplasia syndrome type 2 (MEN-2)
  • Active or history of pancreatitis
  • Severe gastrointestinal disease
  • Pregnancy or planned conception
  • Diabetic retinopathy (rapid glycaemic improvement may worsen retinopathy acutely)

Post-marketing surveillance data published in JAMA Internal Medicine (2024) identified a significantly elevated risk of non-arteritic anterior ischaemic optic neuropathy (NAION) in semaglutide users — a finding now under active review by the FDA.

The Drug Shortage Crisis: A Direct Consequence of Unregulated Prescribing

The global demand surge driven by cosmetic weight-loss use has created critical shortages of semaglutide and liraglutide, directly depriving patients with type 2 diabetes and established cardiovascular risk of their first-line, evidence-based therapies. The HPRA and HSE Ireland have issued repeated supply alerts since 2022. The NHS in the UK has prioritised supply for diabetes management over obesity indications.

Clinicians and patients must understand that obtaining GLP-1 RAs through private online portals for cosmetic weight loss directly displaces supply from those with the greatest clinical need.

Key Safety Warnings

  • Unverified online platforms cannot perform the physical examination, baseline bloods (HbA1c, thyroid function, lipid panel, renal function), or screen for contraindications required before initiation.
  • Compounded semaglutide obtained outside licensed pharmacy networks is not bioequivalent to licensed products and lacks quality assurance. The FDA and MHRA have both issued explicit warnings against compounded GLP-1 products.
  • Dose escalation without clinical oversight significantly increases the risk of severe nausea, vomiting, dehydration, gastroparesis, and acute pancreatitis.
  • Abrupt cessation without structured follow-up results in rapid weight regain — typically exceeding baseline weight within 12 months (STEP-4 extension data, 2022).
  • Sarcopenia risk: Without protein-optimised dietary guidance and resistance exercise, GLP-1 RA-induced weight loss includes significant lean muscle mass — a serious concern, particularly in older adults.

What Safe, Regulated Prescribing Looks Like

Guidance from NICE (TA875 — tirzepatide, 2024; TA664 — semaglutide, 2023), the European Association for the Study of Obesity (EASO), and the Irish Society for Clinical Nutrition & Metabolism (IrSCNM) is explicit: GLP-1 RA prescribing for obesity requires:

  • Baseline BMI ≥30 kg/m² (or ≥27 with weight-related comorbidity)
  • Comprehensive metabolic blood panel prior to initiation
  • Contraindication screening by a qualified clinician
  • Structured dose titration schedule with clinical review at each step
  • Dietary and physical activity counselling throughout treatment
  • Regular monitoring — HbA1c, renal function, hepatic enzymes, cardiovascular risk
  • A clear long-term management plan addressing what happens when medication is discontinued

The Cardiometabolic Dimension

The SELECT cardiovascular outcomes trial (Lincoff et al., NEJM 2023) demonstrated that semaglutide 2.4 mg reduced major adverse cardiovascular events (MACE) by 20% in overweight/obese adults with pre-existing cardiovascular disease. This cardioprotective evidence reinforces the case for these agents being prescribed within a combined cardiology–endocrinology framework — not in isolation by non-specialist platforms.

For patients with both obesity and cardiac risk, integrated care between a Consultant Endocrinologist and Consultant Cardiologist is the gold standard of management.