Peptides for weight loss: How they work and what's available in the UK

It's hard to imagine that a mere five years ago, weight loss medications like Ozempic, Mounjaro and Wegovy weren't yet household names. Back then, they seemed like mysterious substances used by the rich and famous to get in shape before red carpet events.

Fast forward to today, and there's a much greater understanding of just how effective these weight loss medications can be for people from all walks of life (not just celebs). As mainstream awareness grows — yet availability and prices fluctuate — it was only a matter of time before people tried to harness the benefits of GLP-1 medications themselves for cheaper at home. Enter the rising trend of DIY peptides.

But how do peptides actually work for weight loss? Is it actually safe to inject yourself with these substances, and what is actually available and legal in the UK? From the science to the trade-offs and potential side effects, here's everything you need to know about peptides for weight loss.

What are peptides?

Peptides are naturally occurring substances in the body that play a crucial role in many biological functions [1]. Usually composed of a short chain of between 2 and 50 amino acids, they're essentially like a smaller version of proteins. Binding to specific receptors in the body, you can think of peptides like small-yet-mighty drill sergeants telling your organs what to do.

Our bodies produce peptides to assist with everything from regulating hormone production, inflammation and metabolism to supporting muscle development [2]. However, there are some instances in which humans aren't able to produce sufficient peptides to support these processes [3]. For example, people with type 1 diabetes are not able to produce enough of the peptide, insulin, to regulate their blood sugar.

This is where synthetic, therapeutic peptides come in. GLP-1 medications like Ozempic have actually been around for decades, as a life-saving  mechanism to help diabetics supplement their insulin production. Simultaneously, topical synthetic peptides have long been popular in skin and haircare — think collagen peptide products that promise to turn back the clock on your skin or hair.

As science and technology have advanced, there's been greater attention to the potential benefits of synthetic peptides. Biohacking and beauty enthusiasts alike are supplementing peptides for everything from anti-aging and fat burning to longevity.

How peptides support weight loss

As amino acid chains can form in virtually endless ways, there are over 7000 known peptides in the body. However, there are a few in particular that have a notable impact on appetite control and weight reduction, due to the gut-brain connection [4]. These include:

• Glucagon-Like Peptide 1 (GLP-1): Prompts the pancreas to release insulin when blood sugar rises, slows gastric emptying and sends signals of satiety to the brain.
• Glucagon-Like Peptide 2 (GLP-2): Improves your body's ability to absorb and use nutrients from the foods we eat, and strengthens the intestinal lining to protect against inflammation and permeability.
• Glucagon (GCG): Encourages the liver and fat cells to break down stored fats (lipolysis) to be used as alternative energy, producing ketone bodies in the process.
• Peptide tyrosine tyrosine (PYY): Released after eating, this weight loss peptide promotes fullness and helps to regulate blood sugar.
• Ghrelin: Signals to the body that it's time to eat and stimulates appetite (it's what gives you that 'rumbling stomach' feeling)

The main peptides used for weight loss

Clever scientists have found a way to simulate these naturally occurring weight loss peptides in a lab using synthetic ingredients such as yeast cells. These are the active ingredients found in the handful of peptide weight loss medications approved by the FDA and MHRA.

Semaglutide

Belonging to a group of medications called GLP-1 receptor agonists, semaglutide mimics GLP-1 to regulate blood sugar and regulate appetite [5]. It is the active ingredient in the injectable medications Ozempic and Wegovy, as well as the oral version of Wegovy.

Liraglutide

Like semaglutide, liraglutide is a GLP-1 receptor agonist. The difference is in its potency, as semaglutide stays in the body much longer than liraglutide and leads to more significant weight loss [6]. While semaglutide is taken once per week, liraglutide medications like Saxenda must be injected daily.

Tirzepatide

Tirzepatide is slightly different to semaglutide and liraglutide, in that it falls into a category of medications called GLP-1 receptor agonists. These are sometimes referred to as 'twincretins', as they harness the combined benefits of both the GIP and GLP-1 receptors to assist with weight loss [7].

Tirzepatide is the active ingredient in Mounjaro and Zepbound — and thanks to this dual-acting mechanism, there is some evidence to show it's the most effective medication for weight loss on the market [8].

Other weight loss peptides

There are several other injectable peptide medications that are currently being tested across the globe [9]. These include retatrutide (which targets three receptors: GLP-1, GIP, and glucagon); CagriSema (combines GLP-1 with the amylin, cagrilintide) and MariTide (maridebart cafraglutide). While trials show promising results, these peptides for weight loss are not yet approved or officially available.

Concerningly, there have been numerous recent cases of severe liver toxicity amongst people who purchased DIY peptides marketed as 'retatrutide' online [10]. Unlike the prescription medications mentioned above, these counterfeit products are not rigorously tested. Therefore, it's difficult to say exactly what's in them and what they do to the body.

Other unauthorised peptides that are gaining popularity are growth hormone-releasing peptides [11]. Similar to anabolic steroids, these are used to support muscle gain and fat loss. However, they come with significant side effects and safety concerns.

How effective are peptides for weight loss?

When administered as an FDA-approved medication — and prescribed and monitored by a healthcare professional — synthetic peptides are highly effective for weight loss. The exact weight loss statistics vary depending on the type of medication.

Over a 72-week period, patients typically see a 20.9% decrease in body weight on Mounjaro, 20.7% with injectable Wegovy and 16.6% with oral Wegovy [12,13, 14]. These results are even more significant when combined with coaching and lifestyle intervention through a structured weight management program like Juniper. [15]

Meanwhile, due to a lack of clinical evidence, it is very difficult to say how effective DIY, compounded peptide treatments are for weight loss. As these synthetic peptides are not manufactured in a commercial lab for optimal efficacy and dosage, you are unlikely to see reliable results.

Are peptide supplements safe and effective for weight loss?

A distinction must be made between the FDA-approved injectable medications listed above and the growing wave of 'grey market' peptide supplements.

The former are mass-produced by reputable manufacturers such as Novo Nordisk under stringent conditions and are prescribed by a health professional. While these medications are still relatively new, we have hundreds of randomised controlled trials that indicate they are safe and effective for weight loss.

On the other hand, you have experimental home peptide treatments, which you'll often see marketed as 'peptide therapy,' 'peptide doctors, or 'peptide clinic.' These are typically administered via subcutaneous injection, but not under the professional medical advice of a doctor.

A caveat: You can purchase peptides in powdered supplement form. While these are unlikely to be as effective as prescribed weight loss medication, they are typically fairly harmless. Powdered peptide supplements containing creatine and collagen can also be a great adjunct to a healthy diet and exercise for overall wellbeing, energy levels, muscle development and anti-aging [16].

Common side effects of peptide weight loss treatments

While side effects are common with prescription weight loss medications, these are typically mild and temporary. They also involve working alongside a doctor, who will help monitor your symptoms and adjust dosage if necessary.

Gastrointestinal side effects such as diarrhea, vomiting, bloating and nausea are also common with DIY peptide injections — the difference being, you're left navigating it alone and wondering if what you're experiencing is normal [17].

There have also been an increasing number of reported cases of more severe and even life-threatening adverse reactions, such as liver damage and other organ failures, anaphylaxis, hormonal issues and skin infections.

Who can take peptide weight loss treatments in the UK?

In the UK, the eligibility requirements for prescription weight loss peptides depend on the specific medications and whether you access them via the NHS or via private prescription. But, generally, the criteria are a BMI of over 30 (or 27 if you also have a weight-related health condition such as high blood pressure or pre-diabetes) [18].

Meanwhile, there are usually no specific eligibility criteria for DIY peptides bought via compounding chemists, nor do you need a prescription to access them. This can be highly appealing to those who do not meet the criteria for prescription medication but would like to leverage peptides in their weight loss journey. Unfortunately, as home peptide treatments are currently such a Wild West, it's simply not worth the risk.

Are weight loss peptides regulated in the UK?

The aforementioned weight loss medications (Mounjaro, Wegovy and Ozempic) are highly regulated and tightly controlled in the UK. However, this is not the case for DIY peptide treatments.

These exist in a legal and regulatory grey area, as they are not illegal to buy or own. However, they are not approved for human use, and selling them is considered a violation of the Human Medicines Regulations 2012 [19]. As a loophole to get around this, you'll often see phrases like 'for research purposes only' or 'not for human use' splashed across the bottles. Talk about a red flag!

How to access peptide weight loss treatment safely

The best way to avoid safety concerns with peptide treatments is to only access weight loss treatments through a medical doctor — not a personal trainer, nutritionist, aesthetician or any other practitioner.

There are also some red flags to look out for. If you can 'add to cart' without first having a consultation with a doctor, steer clear. Reputable weight loss medication providers will also not market their product as 'peptides.' While regulations vary from country to country, medical weight loss providers in the UK are allowed to list medical brand names. So, you should look for transparency when assessing your options.

When to speak to a healthcare professional about weight loss treatment

In a world that prizes fast results and band-aid solutions, it's easy to be peptide-curious. However, at the end of the day, the potential benefits of peptides are unlikely to be worth the safety concerns. Luckily, that doesn't mean you have to just grit your teeth and slog your way through your weight loss journey.

Even if you think you're unlikely to be eligible for injectable weight loss medications, it's worth a conversation with a doctor. There may be other safe and effective options available to you. For example, the oral medication Orlistat (Alli) has a lower BMI cut-off and can lead to 8% weight loss over six months [20].

No matter your weight loss goals, there is a safe and effective solution available to you. Juniper's Weight Loss Programme is tailored to your specific needs, so you make weight loss work for you — not against you. To check your eligibility and learn more, get started with our short questionnaire here.

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