Injections for Weight Loss - Do They Really Work?

Medically reviewed by Dr Ian Martin — Last updated September 2026

Weight loss injections have rapidly become one of the most talked-about treatments in modern medicine. While effective, if you’re considering injections for weight loss, the real question that matters is what kind of result you can realistically expect, what it takes to maintain it, and what the downsides are.

What Are Weight Loss Injections?

Weight loss injections are a series of jabs injected into your stomach. They often contain Semaglutide or Liraglutide, and work by mimicking hormones your gut releases naturally after eating.

They slow digestion, increase feelings of fullness, and reduce appetite which, over time, helps people eat less without constant conscious restriction.

They’re taken as a weekly injection, with the dose increased gradually over several months. These ‘slimming’ injections are not a quick-fix or magical tool, however. Rather, they are They’re intended to complement other crucial aspects of weight loss, including exercise and a healthy diet.

How Effective Are Weight Loss Injections?

Weight loss injections can be an effective treatment for people living with obesity. Results vary between medications and individuals, but clinical trials have shown significant weight loss compared with lifestyle changes alone.

In a study of nearly 10,000 patients, semaglutide led to an average weight loss of 14% over a year¹. So someone starting at 100kg would typically be down to around 86kg. Tirzepatide led to an average weight loss of 16.5% and 20% in clinical trials at the highest dose (15mg).

Weight loss injections also provide health benefits beyond weight. Some trials found that semaglutide was associated with a 20% reduction in the risk of heart attack and stroke in obese or overweight patients (with a BMI of 27 or above who had existing cardiovascular disease and did not have diabetes²).

But the effectiveness of weight loss injections needs to be considered alongside their potential side effects, costs, and the need for ongoing treatment.

The Downsides of Weight Loss Injections

While weight loss injections can be effective, they are not suitable for everyone. There are several potential downsides you need to consider before starting treatment.

1. Cost: Weight loss injections in Australia can be quite expensive, costing around $380-$700 per month, depending on the medication and dose. They are generally not subsidised by Medicare when prescribed for weight management. Since these treatments are longer-term, the ongoing costs are a really important consideration.
2. Weight regain after stopping: Weight regain can occur when weight loss injections are stopped. Research has found that people who stop semaglutide can regain a significant proportion of the weight they lost, particularly when the medication is not replaced with another long-term treatment approach.
3. Ongoing treatment: For some people, maintaining weight loss requires continued use of medication alongside long-term changes to nutrition, physical activity, and lifestyle. How long treatment should continue will depend on the individual and should be discussed with the treating doctor.
4. Side effects: Weight loss injections can cause side effects, most commonly gastrointestinal symptoms such as nausea, vomiting, diarrhoea, abdominal discomfort, and constipation. For some people, these symptoms can be significant and may lead to dehydration or difficulty eating and drinking. More serious complications, including pancreatitis, can also occur, although these are uncommon. Like anything, it’s important to understand the potential risks before starting treatment.

For these reasons, weight loss injections should not be viewed as a quick fix. They are a medical treatment that needs to be considered alongside your individual health, weight loss goals, treatment preferences, and long-term plans.

Who is Eligible for Weight Loss Injections?

Injections can be a genuinely good fit for people with a smaller amount of weight to lose, people who aren’t candidates for surgery, or people using them as a first step after trying diet and exercise. They may also be used to help someone lose weight before an operation if this is recommended by their doctor.

But it’s important to remember that weight loss injections aren’t a one-size-fits-all solution. Whether they’re suitable for you will depend on things like your BMI, health, medical history and the specific medication being considered.

You’ll also need to think about the long-term. Weight regain is common after stopping these medications, so some people may need ongoing treatment to help maintain their weight loss.

Weight Loss Injections vs Weight Loss Surgery

For people with significant weight to lose, it’s worth knowing how injections compare to surgical results. Weight loss surgery and GLP-1 medications are both effective treatments for obesity, but they deliver different outcomes. One of the biggest differences between the two is the way they influence weight management over time.

Injections suppress appetite while they’re being taken, whereas surgery creates permanent changes to the digestive system and the hormones involved in hunger and satiety that last long after the procedure.

In terms of amount lost, patients often lose more with weight loss surgery, especially looking at the long-term. Research shows that bariatric surgery is associated with greater overall weight loss than injections and medications for patients with moderate to severe obesity.

Learn more about weight loss injections vs weight loss surgery.

Injections for Weight Loss – Do They Really Work?

While effective, weight loss injections are expensive and not sustainable for long-term use. Evidence suggests that as soon as you stop using injections, you may experience rapid weight rebound. Often there is even an overshoot such that patients put on more weight than they originally started with. In a review at a bariatric college meeting, a world expert on the topic suggested that if you start these agents to lose weight, then you need to keep them going lifelong.

Have you been considering weight loss injections as a quick fix? Before you do, we suggest doing research on the side effects and proper use of them. Alternatively, we recommend you look into other more effective methods of weight loss.

Injections for significant weight loss is something that Dr Ian Martin discourages. If you are wanting to start your weight loss journey, we highly recommend looking into weight loss surgery as it is cheaper and more effective than injections in the long-term. To find out more information about this procedure, or to get started on the path to better health, contact the team at Brisbane Weight Loss Surgery today.

References:

1. Ng CD, Divino V, Wang J, Toliver JC, Buss M. Real-world weight loss observed with semaglutide and tirzepatide in patients with overweight or obesity and without type 2 diabetes (SHAPE). Adv Ther. 2025;42(11):5468–5480. doi:10.1007/s12325-025-03340-2.
2. Lincoff AM, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes. New England Journal of Medicine. 2023;389:2221–2232. doi:10.1056/NEJMoa2307563