GLP-1 Agonists: Complete Guide to Drugs, Uses & Side Effects

A class of medication that started as a diabetes treatment has become a household name thanks to its weight loss effects. But with that fame comes confusion—about which drugs are which, who can take them, and what the real risks are.

Drug class: Glucagon-like peptide-1 receptor agonists ·
Number of FDA-approved agents: 7 ·
Primary indications: Type 2 diabetes, obesity (some agents) ·
Year of first approval: 2005 (exenatide) ·
Common brand names: Ozempic, Victoza, Trulicity, Wegovy, Saxenda, Byetta

Here is a summary of the key facts about this drug class.

What drugs are GLP-1 agonists?

List of approved GLP-1 receptor agonists

• Exenatide (Byetta, Bydureon) – twice daily injection or once weekly
• Liraglutide (Victoza, Saxenda) – once daily injection
• Dulaglutide (Trulicity) – once weekly injection
• Semaglutide (Ozempic, Wegovy, Rybelsus) – once weekly injection or once daily oral
• Lixisenatide (Adlyxin) – once daily injection

Seven distinct agents were approved as of 2021, according to a SAGE Journals review (peer-reviewed pharmacology). Short-acting versions (like twice-daily exenatide) tend to cause more side effects than long-acting ones, per NCBI Bookshelf clinical reference.

How GLP-1 agonists work

GLP-1 stands for glucagon-like peptide-1, a natural incretin hormone. The drugs mimic it, boosting insulin secretion when blood sugar is high, slowing gastric emptying, and signalling fullness to the brain. NCBI Bookshelf clinical pharmacology resource explains the mechanism as primarily glucose-dependent, which reduces hypoglycemia risk.

GLP-1 full form and structure

The full name is glucagon-like peptide-1 receptor agonist. Structurally, these are peptides (or peptide analogues) that bind to GLP-1 receptors. The first approved, exenatide, is a synthetic version of a compound found in Gila monster saliva. NCBI Bookshelf provides the biochemical background.

Are GLP-1 and Ozempic the same?

What is Ozempic?

Ozempic is the brand name for semaglutide, a GLP-1 agonist. It is approved in Ireland as an adjunct to diet and exercise for adults with insufficiently controlled type 2 diabetes, per Oireachtas supporting documentation (Irish parliamentary records). The same molecule, under the brand Wegovy, is approved for weight management. Ozempic is available in 0.25 mg, 0.5 mg, and 1 mg strengths, with the 1 mg dose experiencing supply constraints in 2023, according to HPRA shortage letter (Irish medicines regulator).

How does Ozempic compare to other GLP-1 agonists?

Ozempic is not all GLP-1 agonists. Other drugs include Trulicity (dulaglutide), Victoza (liraglutide), and Byetta (exenatide). Head-to-head evidence from SAGE Journals shows that once-weekly exenatide has the lowest risk of vomiting, while semaglutide tends to produce greater weight loss. The key difference: only semaglutide (Wegovy) and liraglutide (Saxenda) are FDA-approved specifically for obesity; Ozempic is approved only for diabetes, though it is used off-label for weight loss.

The pattern: only two agents carry a dedicated weight-loss label, and those are at higher doses. The trade-off: higher doses increase gastrointestinal side effects but also boost weight reduction.

Who cannot take GLP-1?

Contraindications for GLP-1 agonists

• Personal or family history of medullary thyroid carcinoma (MTC) (NCBI Bookshelf)
• Multiple endocrine neoplasia type 2 (MEN 2) (NCBI Bookshelf)
• Severe gastrointestinal disease (e.g., gastroparesis) (PubMed)
• Pregnancy and breastfeeding (caution advised) (NCBI Bookshelf)

The implication: screening for these contraindications is essential before prescribing.

Why older people quit GLP-1?

Older adults often discontinue GLP-1 agonists due to gastrointestinal side effects (nausea, vomiting, diarrhea), difficulty with injections, and cost. The PubMed meta-analysis notes that gastrointestinal adverse events are the most common cause of discontinuation across all age groups. Additionally, the HSE restricts reimbursement to patients with full GMS and LTI diabetes eligibility, as per HSE circular (reimbursement policy), meaning cost can be a barrier.

What organ is Ozempic hard on?

Ozempic (semaglutide) can affect the pancreas (risk of pancreatitis) and kidneys. PubMed reports rare but serious cases of acute pancreatitis and gallbladder disorders. The NCBI Bookshelf also warns about delayed gastric emptying, which complicates anaesthesia and colonoscopy prep.

What GLP-1 is available in Ireland?

List of GLP-1 agonists available in Ireland

• Liraglutide (Saxenda, Victoza) – available, Victoza for diabetes, Saxenda for weight loss
• Semaglutide (Ozempic, Wegovy) – Ozempic for diabetes, Wegovy for weight loss (supply constrained)
• Dulaglutide (Trulicity) – for diabetes
• Exenatide (Byetta) – for diabetes

All are prescription-only, regulated by the HPRA (Irish medicines regulator). The HSE restricts reimbursement for Victoza, Ozempic, and Trulicity to people with full GMS and LTI diabetes eligibility, as per HSE circular (reimbursement policy).

How to get GLP-1 in Ireland?

You need a prescription from a doctor. For diabetes, GPs can prescribe under the HSE scheme. For weight loss, Wegovy is available but at full private cost (around €200–€300 per month). Supply of Ozempic 1 mg was interrupted in September 2023, per HPRA shortage letter, so availability may vary.

What are the side effects of GLP-1 agonists?

Common side effects

• Nausea, vomiting, diarrhea, constipation, abdominal pain (NCBI Bookshelf)
• These affect up to 30–50% of patients, especially in the first weeks (SAGE Journals)

Serious side effects

• Pancreatitis (inflammation of the pancreas) (PubMed)
• Gallbladder disease (gallstones, cholecystitis) (PubMed)
• Kidney injury (acute kidney injury reported) (PubMed)
• Thyroid C-cell tumours (contraindication in MTC) (NCBI Bookshelf)

How to manage side effects

Dose titration (starting low and increasing gradually) reduces nausea. Taking injections with meals and staying hydrated also help. NCBI Bookshelf advises that side effects often decrease over time. If severe, patients should consult their doctor.

“GLP-1 receptor agonists are a class of medications that lower blood sugar by mimicking the action of a hormone called glucagon-like peptide-1.”

Cleveland Clinic (via NCBI Bookshelf, clinical reference)

“The most common adverse effects are gastrointestinal, particularly nausea, vomiting, and diarrhea. These tend to be dose-dependent and often improve with continued use.”

StatPearls (NCBI Bookshelf, peer-reviewed medical education)

“In Ireland, Ozempic is indicated for type 2 diabetes. Use for weight management is off-label and not reimbursed under the GMS scheme.”

SCHOM (Irish health professional guidance)

For patients in Ireland, the decision to start a GLP-1 agonist comes down to a trade-off: meaningful glucose control and weight loss versus GI side effects, injection burden, and cost. If you have diabetes and meet HSE criteria, Ozempic or Trulicity may be accessible. If you are seeking weight loss without diabetes, Wegovy is available but at a significant out-of-pocket expense. The shortage of Ozempic 1 mg means that supply may be unreliable, so check with your pharmacy. Your GP can help you navigate the options based on your health profile and budget.

For a detailed overview of available medications and their effects, refer to this comprehensive guide to GLP-1 agonists.

Frequently asked questions