Peptides for Weight Loss and Muscle: What Women in Perimenopause Actually Need to Know

If you have spent any time on Instagram or TikTok lately, you have probably seen someone talking about peptides. Injectable vials. Bold claims about fat loss and muscle growth. A fitness influencer telling their followers the product is "not approved for human use, do with it as you will."

Before we get into it, one thing worth knowing: you are probably already familiar with peptides, just not by that name. Wegovy and Mounjaro, the medications that have taken the weight loss world by storm over the past couple of years, are both peptides. They are approved by the TGA, extensively studied, and prescribed under medical supervision. They are genuinely effective for the people they are appropriate for.

The peptides being sold online right now are a completely different story.

As a dietitian working with women through perimenopause and weight loss, this is a conversation I am having more often. So let's dive into it in more detail...

What are these peptides, and what are people claiming?

The products being sold online, often with names like Tesamorelin, Sermorelin, Ipamorelin, and CJC-1295, work by stimulating your body to release more growth hormone. The marketing claim is that more growth hormone means more fat loss and more muscle. Sounds straightforward. The problem is that the science does not really back it up.

AOD-9604 is a good example of how this plays out. It is a growth hormone fragment that made headlines in Australia when it was injected by Essendon AFL players in the 2013 supplements scandal (as a Bombers supporter I remember this VERY clearly!!!). It worked in animal studies. It went through multiple human clinical trials. It never made it to market because the larger, more rigorous trials did not produce meaningful weight loss results.

That gap between what works in a lab and what holds up in real human trials is exactly where most of the online peptide marketing lives.

Peptides: On the muscle growth claim

Here is the honest answer: growth hormone is not the primary driver of muscle growth in adults. The things that actually build muscle are resistance training, eating enough protein, and having the right hormonal environment.

A systematic review published in the Annals of Internal Medicine analysed 27 randomised controlled trials on growth hormone in healthy adults. Lean body mass increased in participants who received growth hormone compared to those who did not, but strength and exercise capacity did not change meaningfully.

When researchers looked closely, much of the lean mass increase appeared to be fluid and connective tissue rather than actual new muscle. You cannot inject your way around lifting weights and eating enough protein.

Peptides for fat loss:

Growth hormone does increase the release of fatty acids from fat cells, and that process gets used heavily in marketing language about "burning fat." But releasing fat from fat cells is not the same as losing body fat.

A study published in the Journal of Clinical Endocrinology and Metabolism gave growth hormone to obese subjects alongside dietary restriction for 11 weeks. There were no significant differences in total weight loss or percentage of body fat lost compared to placebo, even though growth hormone caused a notable increase in circulating fatty acids. In other words, more fat was being released into circulation, but actual fat loss was identical to placebo.

Think of it like this: opening the door of a room does not mean anything leaves the room. The fatty acids being released still need to be burned off, or they simply get stored again.

The safety issue happening right now in Australia

Beyond the question of whether these peptides work, there is a real safety concern, and it goes beyond the marketing claims.

The TGA issued a formal warning about unapproved peptide products, including CJC-1295 and others being sold online. The regulator flagged significant regulatory and public health risks, noting that the use and supply of these products is being actively promoted through social media platforms.

What that means in practice: products that have not gone through TGA assessment have not been evaluated for safety, quality, or what is actually in them. Researchers who have tested unregulated injectable products purchased online have found contamination with heavy metals including lead and arsenic. You are not just taking a gamble on whether it works. You are taking a gamble on what is actually in the vial.

This is the core distinction. TGA-approved medicines like semaglutide and tirzepatide have undergone extensive clinical trials and are prescribed with appropriate medical oversight. The peptides sold through social media and gym networks have not. They are not the same category of product.

What actually works for weight loss in perimenopause

The fundamentals of fat loss do not disappear in perimenopause, but the context shifts. Hormonal changes affect where fat is stored (often the belly), how sleep quality changes, how your blood sugar responds to meals, and how easily you maintain muscle. None of this means fat loss is impossible. It means your strategy needs to account for these factors.

It is important to note that these lifestyle factors need to be addressed even if you are taking approved medications such as Wegovy or Mounjaro.

These are the key lifestyle factors that I focus on with my clients and are the same for my clients who are on weight loss medications and those who aren't:

Protein at every meal. This is the single most impactful change for most of the women I work with. Adequate protein supports muscle retention, keeps you fuller for longer, and reduces the afternoon energy crash that leads to reactive eating later in the day.

Meal structure that prevents under-fueling. Most of my clients arrive eating too little during the day and too much in the evening. This is not a willpower problem. It is a predictable response to irregular fuelling. Eating more at the right times is often the fix, not eating less.

A system that works on your worst week, not just your best. Perimenopause does not care about your schedule. The approach needs to be flexible depending on your capacity, not fall apart when life gets busy.

Sleep and stress as part of the weight loss conversation. These are not separate issues. They directly affect appetite, cravings, and your body's ability to lose fat. A nutrition plan that ignores them is working with one hand tied behind its back.

The bottom line

Peptides sold online are not a shortcut to fat loss or muscle growth. The animal research does not translate reliably to humans, the fat loss mechanism does not hold up to scrutiny, and the safety profile of unregulated products is genuinely unknown.

This is not to say that things in this space won't change but at the moment, with the research we have and the lack of regulations in place means there are risks associated with using these products.

However, regardless of any medications or products you might be using, the fundamentals will always still apply: protein, meal structure, a flexible and sustainable system, and support that accounts for where you are hormonally and in life.

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If you are navigating weight loss in perimenopause and you are not sure where to start, book a free Kickstart Call and we will work through what is actually going on for you and what would make the most difference.