What Are GLP-1 Receptor Agonists? A Prescriber's Guide
A clinical overview of GLP-1 receptor agonists — how they work, current approved indications, and what prescribers need to know about semaglutide and tirzepatide.
GLP-1 receptor agonists have rapidly become one of the most significant drug classes in modern prescribing. Whether you run an independent pharmacy, an online prescribing service, or a weight management clinic, understanding the pharmacology behind these medications is essential for safe, effective patient care.
The incretin system
GLP-1 (glucagon-like peptide-1) is a naturally occurring incretin hormone released by L-cells in the small intestine after eating. In healthy physiology, GLP-1 performs several functions: it stimulates insulin secretion in a glucose-dependent manner, suppresses glucagon release, slows gastric emptying, and acts on hypothalamic receptors to promote satiety.
The problem is that native GLP-1 has a half-life of roughly two minutes — it is rapidly degraded by the enzyme dipeptidyl peptidase-4 (DPP-4). GLP-1 receptor agonists are synthetic analogues engineered to resist this degradation, giving them dramatically longer durations of action.
How GLP-1 receptor agonists work
These drugs are incretin mimetics. They bind to and activate the GLP-1 receptor, producing the same downstream effects as the native hormone but in a sustained, pharmacologically meaningful way:
- Appetite suppression — central action on hypothalamic GLP-1 receptors reduces hunger and increases feelings of fullness
- Delayed gastric emptying — slows the rate at which food leaves the stomach, contributing to reduced caloric intake
- Glucose-dependent insulin secretion — stimulates beta-cell insulin release only when blood glucose is elevated, reducing hypoglycaemia risk
- Glucagon suppression — reduces hepatic glucose output in the postprandial state
Tirzepatide (Mounjaro) adds a second mechanism: it also activates the GIP (glucose-dependent insulinotropic polypeptide) receptor. This dual incretin approach appears to produce greater weight loss and glycaemic improvement than GLP-1 receptor activation alone, though the precise contribution of GIP agonism is still being studied.
Currently approved medications
The two GLP-1 receptor agonists most relevant to prescribers in weight management are:
Semaglutide (Wegovy) — a once-weekly subcutaneous injection approved by the MHRA for chronic weight management in adults with a BMI of 30 kg/m² or greater, or 27 kg/m² with at least one weight-related comorbidity. Semaglutide is also available as Ozempic for type 2 diabetes management at lower doses.
Tirzepatide (Mounjaro) — a once-weekly subcutaneous dual GIP/GLP-1 receptor agonist. Originally approved for type 2 diabetes, tirzepatide has also received approval for chronic weight management based on the SURMOUNT trial programme.
Both drugs follow structured titration schedules, starting at lower doses and escalating over several weeks to reach therapeutic maintenance levels. This approach is designed to improve gastrointestinal tolerability — one of the most common reasons patients struggle with treatment.
Pharmacokinetics: why it matters for patient support
Understanding basic pharmacokinetic (PK) principles is more than academic — it directly informs how you support patients day to day.
Semaglutide has a half-life of approximately seven days, reaching steady-state concentrations after four to five weeks of weekly dosing. Tirzepatide has a similar half-life of roughly five days. Both drugs show peak plasma concentrations one to three days after injection.
This PK profile has practical implications:
- Side effects cluster around peak concentrations — nausea and gastrointestinal symptoms tend to be worst in the one to three days following injection, then improve as drug levels trough towards the end of the dosing interval
- Dose escalation triggers new peaks — each titration step produces a higher peak concentration, which is why side effects often return or worsen at dose increases
- Steady state takes weeks — patients need to understand that their body is still adjusting during the first month at any given dose
This is precisely why structured patient support matters. When prescribers can monitor how patients feel across the dosing cycle — not just at a monthly review — they can intervene earlier, offer targeted advice, and make better titration decisions. Cadence was built around this principle: daily patient check-ins mapped to the pharmacokinetic cycle give prescribers real-time visibility into side effects, adherence, and wellbeing.
The bigger picture
GLP-1 receptor agonists represent a genuine step change in obesity pharmacotherapy. But the drug alone is not the full picture. Real-world adherence data consistently shows that a significant proportion of patients discontinue treatment within the first six months — often due to manageable side effects or unmet expectations.
For prescribers across all settings — whether you are dispensing in a community pharmacy, prescribing via an online platform, or managing patients in a specialist clinic — understanding the pharmacology is the foundation. Pairing that knowledge with structured patient support is what turns a prescription into a sustained outcome.
If you are prescribing GLP-1 receptor agonists and want to see how pharmacokinetic-informed patient monitoring works in practice, book a demo to explore the Cadence platform.