Your questions on GLP-1s and peptides answered (by a medical doctor)

What are GLP-1s?

“GLP-1 stands for glucagon-like peptide-1, a hormone your body naturally produces after eating,” says Dr Andy. “It helps regulate blood sugar levels and appetite. GLP-1 medications work by mimicking this hormone, helping people feel fuller for longer, quieten food noise, and slow digestion.”

Did you know? GLP-1s were originally developed to treat diabetes type 2, not weight loss. The weight-loss effects were observed during diabetes treatment and later became a major focus.

Are GLP-1s and peptides the same thing?

Peptides are everywhere in our bodies. Insulin, collagen fragments, signalling molecules, and GLP-1 are all peptides; GLP-1 is just one member of a huge family of what scientists call ‘highly targeted, short-lived structural and functional workhorses’. Dr Andy notes, “While GLP-1 medications are peptide-based drugs, the term ‘peptides’ can also refer to many other compounds used in medicine, research, and in the performance, anti-ageing, and cosmetic spaces where they are an absolute buzz, but where they are often unregulated.” But today we are focusing on weight loss.

Handy definitions

• Peptides are short chains of amino acids, many that act as signalling molecules in the body. There are many different peptides with different functions.
• GLP-1 (glucagon-like peptide-1) is a naturally occurring peptide hormone that helps regulate blood sugar and appetite.

What are the main types of weight-loss medications?

While people often group these medicines together as ‘GLP-1s’, there are actually different types available for weight loss and not all of them are regulated. Let’s talk through the main medications currently being prescribed and spoken about with every scan of social media. 

1. Semaglutide / Brand names: Wegovy, Ozempic

Semaglutide is a GLP-1 receptor agonist, meaning it mimics the naturally occurring GLP-1 hormone. It is used to treat both type 2 diabetes and obesity. It is available under different brand names, including Ozempic for type 2 diabetes and Wegovy primarily for weight loss. By activating GLP-1 receptors, semaglutide helps to reduce appetite, slow digestion and increase feelings of fullness, which can support weight loss and improve blood sugar control.

2. Tirzepatide / Brand name: Mounjaro

Tirzepatide is a medication used to help manage type 2 diabetes and support weight loss. Unlike traditional GLP-1 medicines that target a single hormone, tirzepatide is a dual GIP/GLP-1 agonist, meaning it activates two natural hormones involved in appetite, digestion, blood sugar regulation and metabolism. By targeting both pathways, it can help reduce hunger, increase feelings of fullness, improve blood sugar control and support significant weight loss in some people.

3. Retatrutide

This is an investigational (not yet approved) weight-loss and diabetes medication currently being studied in clinical trials. Unlike GLP-1 medications such as semaglutide, or dual-action medicines such as tirzepatide, retatrutide targets three hormones involved in appetite, blood sugar regulation and metabolism: GLP-1, GIP and glucagon. Because it acts on all three pathways, it is often called a "triple agonist" or "Triple G" medication. Researchers are investigating whether this approach may lead to greater weight loss and metabolic benefits than current treatments, but it has not yet been approved for general use.

Who are these medications designed for?

These medications are not intended for anyone looking to shed some weight. In Australia, these medicines are generally prescribed by a health professional for people living with obesity or for some who are overweight and have weight-related health conditions. “Your doctor will take into consideration a lot of other factors to assess their suitability for you, including your medical history, current medications, health risks and long-term goals,” Dr Andy explains.

They are not appropriate for everyone and chatting to your doctor is key. A “TikTok doctor” doesn’t count either, so if you think they may be suitable,  see a medical professional that can assess you based on you.
Dr Andy

How are these medications changing how obesity is treated?

Because they target some of the biological processes involved in hunger and fullness, medications that target the GLP-1 receptors are fundamentally changing the way obesity is treated. Dr Andy explains that, “Traditionally, weight management has focused heavily on diet and exercise alone (still very important) but researchers now understand that hormones also play an important role in regulating appetite and body weight. By mimicking naturally occurring hormones that help people feel fuller for longer, GLP-1 and related medications have provided a new treatment option for some people living with obesity. While they aren't suitable for everyone and are most effective when combined with permanent healthy lifestyle changes, their emergence has helped shift the conversation around obesity from one of willpower alone to a more comprehensive understanding of how the body regulates weight.”

Will I regain weight if I stop taking GLP-1 medications?

The current evidence suggests eventually, most people will. The medications don't permanently change the biological systems that influence appetite and weight regulation. This means, when treatment stops, hunger signals often return and the effects on fullness and food intake can diminish hence why weight gain can occur.

“That's why experts increasingly view obesity as a long-term health condition that may require ongoing management” Dr Andy says. “For some people, this may include continued medication under the guidance of a healthcare professional, alongside nutrition, exercise, sleep and behaviour-support strategies.”

What side effects can occur?

Like all medicines, taking GLP-1 medications may cause side effects. The most common are related to the digestive system.

Common side effects include:

• Nausea
• Vomiting
• Diarrhoea
• Constipation
• Stomach pain or discomfort

More serious side effects are uncommon but can occur, which is why these medications should always be used under medical supervision.

If you're considering a GLP-1 or related medication, speak with your doctor about the potential benefits and risks for your individual circumstances.

Are all peptides approved medicines?

This one is important because it is a capital NO.

While some peptides are approved medicines that have undergone years of testing and regulatory review, many others being promoted online have not.

You may see social media posts or websites advertising peptides for weight loss, muscle gain, anti-ageing or performance enhancement. Some of these products are experimental compounds still being studied in clinical trials. Others may not have been approved for use by Australia's Therapeutic Goods Administration (TGA) at all.

Because these products are often sold through unregulated channels, there may be concerns about their quality, safety, purity and effectiveness.

A reminder from our health team: It's important to speak with a healthcare professional before taking any medication, especially products that haven't undergone the rigorous testing and approval processes used to assess their safety and effectiveness.

The Australian TGA has specifically warned that many peptide products sold online:³

• are unapproved
• may contain unknown ingredients
• may be poorly labelled
• may not meet Australian safety standards
• may be contaminated or non-sterile.

The world of peptides can seem overwhelming, especially when social media is full of miracle claims and misinformation. While these medications are a positive advance in obesity and diabetes treatment, they're not a magic fix, and they're certainly not all the same. The best place to get advice about whether a treatment is right for you is from a qualified healthcare professional who can help you weigh up the benefits, risks and alternatives.