What are weight loss injections, and are they safe?

Over the last few years, weight loss injections have taken the world by storm. Originally developed to manage type 2 diabetes, GLP-1 receptor agonist (GLP-1 RAs) are now prescribed for obesity treatment. But how exactly do they work, and more importantly, are they safe to use?

Whether you’re taking weight loss injections, considering them as a treatment, or just curious, here are some things you should know.

This article covers:

• What are weight loss injections?
• How did GLP-1 drugs get from treating diabetes to obesity?
• Who can take weight loss injections?
• How do weight loss injections work?
• Fun fact: Weight loss injections are derived from monsters
• Are weight loss injections safe?
• What are the side effects to weight loss injections?

What are weight loss injections?
 

Weight loss injections are a group of drugs known as glucagon-like peptide-1 receptor agonists (GLP-1 RAs). Despite the recent media presence, the drugs themselves aren’t particularly new. The very first GLP-1 agonist medication, exenatide, was approved in the early 00s to treat type 2 diabetes [1].

In 2014, the FDA approved liraglutide for use as a weight loss medication for obesity [2,3]. Obesity is a chronic medical condition where a person has excess body fat, and a body mass index (BMI) of over 27.5 or 30, depending on your family background [4]. It’s linked to heart disease, high blood pressure, kidney disease, and other health conditions.

GLP-1 drugs can help patients lose between 15-25% of their body mass [5]. The drugs help you lose body weight by suppressing your appetite, regulating your blood sugar levels, and slowing down your digestion. They should be used as part of a reduced-calorie diet, with regular exercise.

 

How did GLP-1 drugs get from treating diabetes to obesity?
 

Over time, researchers noticed that people taking GLP-1-mimicking antidiabetic drugs were losing weight [6]. While other antidiabetic drugs didn’t have this effect. So they began studying what would happen if obese people who weren’t diabetic took the medications.

The results were impressive. Patients lost a statistically significant amount of weight, similar to if they had undergone gastric bypass [7]. The difference was the medication was considered much less invasive than surgery.

Once liraglutide was approved for obesity treatment, several other similar medications were developed. As the medical views of obesity changed to a chronic condition, not just a lifestyle.

 

Who can take weight loss injections?
 

Weight loss injections are not suitable for everyone. According to the NHS, you should meet a specific set of criteria established by medical professionals:

• BMI over 35, or BMI over 30 with weight-related health problems.
• Tried and struggled with lifestyle changes like diet and exercise.
• Not pregnant or breastfeeding.
• No history of eating disorders, pancreatitis, or thyroid cancer.

Always get a referral and prescription from a qualified healthcare professional.

To be completely certain if weight loss injections are suitable for you, check with your GP and ask for a referral. Always get your medications via a qualified healthcare professional service – either the NHS or private healthcare provider.

Any other option is illegal, and unsafe.

 

How do weight loss injections work?

Weight loss injections work by mimicking the GLP-1 hormone. “What is a GLP-1 hormone?”, I hear you cry.

GLP-1 is a peptide hormone responsible for insulin release, decreasing blood sugar levels, signalling when you are full and, as a result, suppressing your appetite [8].

We are filled with millions of tiny proteins called receptors that tell our bodies what to do next. When certain chemicals (known as agonists) bind to the receptors, they produce a response. Agonists can be natural, like dopamine, vitamin D, or GLP-1. But they can also be synthetic like morphine and – you guessed it – GLP-1 receptor agonist injections.

GLP-1 typically has a very short half-life (meaning the molecule decomposes after a few minutes), which makes them unsuitable for medications.

So, researchers developed drugs that can act on the same receptors as GLP-1, triggering the same response. The bonus of these synthetic drugs is that they have much longer half-lives, so you only have to inject them daily or weekly.

 

Fun fact: Weight loss injections are derived from monsters
 

Not “hiding under your bed” monsters, but rather, a large, venomous lizard known as the Gila monster. Native to Central America, the Gila monster only eats a couple of times in spring, and not again for the whole year.

Lizards aren’t usually venomous, so scientists were fascinated as to whether there was a connection between the Gila monster’s eating habits and its venom. Sure enough, in 1990s, a molecule was isolated that had a similar effect to GLP-1 in mice. But with a much longer half-life. The scientist who discovered the molecule, John Eng, named it exendin-4 [9].

Weirdly, Eng struggled to find a pharmaceutical company that was interested in the compound. Eventually, the synthetic version named exenatide was approved by the FDA in 2005 [7]. Now the GLP-1 RA drug market is expected to be worth over $100 billion by 2030 [10].

Are weight loss injections safe?
 

If used and monitored correctly – yes. Drugs like semaglutide and trizepatide (Ozempic/Wegovy and Mounjaro) were initially synthesised to treat type 2 diabetes. So they’ve been around for over 20 years, with plenty of clinical trials to back up their safety [7].

Where they stop being safe, is if the medications are abused or have been obtained from unregulated sources. You should only get weight loss injections from specialist weight management clinics that work with registered GPs.

What are the side effects to weight loss injections?
 

As with any medication you may experience some side effects. The most common side effects are gastrointestinal, and other side effects are those associated with rapid weight loss such as loss of muscle mass and “Ozempic face” [5].

Five common side effects of weight loss injections

1. Nausea
2. Bloating
3. Vomiting
4. Constipation
5. Diarrhoea

For some people the symptoms go away with time, for others they become unbearable and need to stop the treatment. A lower dose can help mitigate these symptoms.

There may be other side effects that aren’t so obvious.

GLP-1 injections can affect your:

• Cholesterol
• Kidney health
• Liver health
• Pancreas
• Nutrient levels

 

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References

1. Hamed K, Alosaimi MN, Ali BA, Alghamdi A, Alkhashi T, Alkhaldi SS, et al. Glucagon-Like Peptide-1 (GLP-1) Receptor Agonists: Exploring Their Impact on Diabetes, Obesity, and Cardiovascular Health Through a Comprehensive Literature Review. Cureus. 16: e68390. doi:10.7759/cureus.68390
2. Nuffer WA, Trujillo JM. Liraglutide: A New Option for the Treatment of Obesity. Pharmacother J Hum Pharmacol Drug Ther. 2015;35: 926–934. doi:10.1002/phar.1639
3. Pi-Sunyer X, Astrup A, Fujioka K, Greenway F, Halpern A, Krempf M, et al. A Randomized, Controlled Trial of 3.0 mg of Liraglutide in Weight Management. N Engl J Med. 2015;373: 11–22. doi:10.1056/NEJMoa1411892
4. Obesity. In: nhs.uk [Internet]. 23 Nov 2017 [cited 12 Jun 2025].
5. Reiss AB, Gulkarov S, Lau R, Klek SP, Srivastava A, Renna HA, et al. Weight Reduction with GLP-1 Agonists and Paths for Discontinuation While Maintaining Weight Loss. Biomolecules. 2025;15: 408. doi:10.3390/biom15030408
6. Moore PW, Malone K, VanValkenburg D, Rando LL, Williams BC, Matejowsky HG, et al. GLP-1 Agonists for Weight Loss: Pharmacology and Clinical Implications. Adv Ther. 2023;40: 723–742. doi:10.1007/s12325-022-02394-w
7. Prasad-Reddy L, Isaacs D. A clinical review of GLP-1 receptor agonists: efficacy and safety in diabetes and beyond. Drugs Context. 2015;4: 212283. doi:10.7573/dic.212283
8. Drucker DJ. Mechanisms of Action and Therapeutic Application of Glucagon-like Peptide-1. Cell Metab. 2018;27: 740–756. doi:10.1016/j.cmet.2018.03.001
9. Gila monster: meet the lizard whose venomous bite is saving lives | Natural History Museum. [cited 21 May 2025].
10. Manalac 2 min read | Tristan. GLP-1 Receptor Agonist Market to Reach $125B by 2033: GlobalData. In: BioSpace [Internet]. 20 May 2024 [cited 13 Jun 2025].