Medical weight loss treatments that work

We review weight loss drugs such as Saxenda and meal replacements such as Optifast.

Why weight? See your doctor

We all know that lifestyle changes – healthy diet and exercise – are the ideal way to lose weight and maintain weight loss. There are other physical and mental health benefits, too, but many people with obesity find these changes difficult to stick to.

If this is you, consider getting help from your GP.

There are two main options they can help you with:

While not a substitute for a healthy lifestyle, and there are no guarantees of weight loss, medical weight loss options can provide a useful additional tool to help people manage their weight. However, they don't come cheap – you're looking at upwards of $100 per month for medication, and $300 for meal replacements. 

Track your progress with a fitness tracker. We review models from Apple, Fitbit, Samsung, Garmin and more in our fitness tracker and smartwatch reviews.


Saxenda (liguratide), Xenical (orlistat) and Duromine (phentermine) are the only medicines approved for weight loss in Australia – and none are government-subsidised on the pharmaceutical benefits scheme (PBS) so you'll have to pay full price.

Doctors can prescribe these for people with a BMI over 30, or people with a BMI of 27–30 and weight-related conditions such as pre-diabetes, type 2 diabetes, high blood pressure, high cholesterol or sleep apnoea. 

Studies have found that typical weight loss is around 3–5kg, though results vary widely and can be greater than this or have no effect. Apart from weight loss, there may be other health improvements, including blood glucose, blood pressure and cholesterol levels.

It's best to think of these medicines as tools to help you lose weight via a reduced energy diet and exercise plan.

Xenical (which is the brand name for orlistat) works in your stomach and intestine by preventing your body from absorbing as much as 30% of the fat you eat, helping to lose weight.

It helps you lose weight when used in conjunction with a reduced-fat diet and exercise program. Xenical is taken when you're eating fatty food, so you'll usually take a capsule with each of the three main meals a day (unless you know the meal you're eating contains no fat).

When using the drug, a really fatty meal can have you rushing for the toilet. Unpleasant side effects include oily bowel movements and seepage, flatulence, faecal incontinence, diarrhoea and abdominal pain. As such, you must limit the fat that you eat in a day to less than 12g in each meal, and no more than 40g per day. A McDonalds Big Mac contains 28g of fat and a medium fries contains 15g – so it can add up pretty quickly.

On the other hand, if you simply replace fat with sugar you won't lose much weight.

Apart from the gastrointestinal side-effects mentioned above, other potential effects include reduced vitamin absorption (you should take a vitamin supplement), headache and kidney stones.

Xenical is available over the counter for around $100 a month (if taken three times a day).

Saxenda is based on a human hormone that suppresses appetite, and you inject it yourself daily. It's prescription only, and is not subsidised by the PBS – it costs around $400 per month by private prescription.

The main side effects are nausea, vomiting, diarrhoea and constipation. Less common, but more serious, side-effects include hypoglycaemia (especially for people taking diabetes medication), pancreatitis, gallbladder disease, renal failure and suicidal thoughts.

At almost $5000 per year for an average weight loss of around 5–6kg, the cost vs benefit needs to be considered.

Duromine (phentermine) is an amphetamine-like drug that helps with weight loss by suppressing appetite. It's not on the PBS, and costs around $100–140 per month, depending on the strength of the dose.

Like all amphetamines, phentermine side effects include tachycardia, palpitations, insomnia, anxiety and elevated blood pressure.

In the US, phentermine is available in combination with anti-epilepsy drug topiramate (Topamax and generic), which also works as an appetite suppressant. The weight loss with the combination drug, known as Qsymia, is greater than with phentermine alone.

While side-effects are relatively rare, some are potentially serious, and include headaches, palpitations, insomnia, paresthesia (tingling, numbness, pins and needles), depression and suicidal thoughts, birth defects and serious kidney and eye problems. An Australian study of 103 people had 61 drop out, including 41 because they couldn't tolerate the side-effects.

Qsymia was rejected in Europe due to safety concerns – in particular the cardiovascular and mental health effects. The combination hasn't been approved by the TGA for weight loss in Australia. While the individual drugs may be prescribed "off label" by a doctor and taken together when other treatments have failed or are unsuitable, the TGA has warned about serious risks when topiramate is used for weight loss.

Very low energy diet (VLED)

A very low energy diet (usually called very low calorie diet, or VLCD, on packaging) is one where you replace all your meals with specially formulated meal replacement products, including shakes, soups and snack bars.

VLEDs are very well-studied compared to other weight loss products, and have been used in clinical settings for more than 40 years.


Some of the main brands include Optifast, Optislim, KicStart and Tony Ferguson from pharmacies, and will cost you about $7.50–10.50 a day (though you'll save money on other food). Isagenix is a more expensive version available from resellers for around $500 a month.

How they work

The products are low in carbohydrate, which helps keep the hunger pangs at bay while also causing a mild ketosis, where the body burns fat as fuel.

A VLED is defined as up to 3350kJ per day. This sort of program generally lasts 8–16 weeks (though it can be longer) with weight loss of 1.5 to 2.5 kg per week – and should be supervised by a doctor or dietitian. 

Meal replacement foods for a VLED typically provide in the range of 2000–2500 kJ per day when you have three as recommended. You can add certain other foods, particularly vegetables. While the strict version of the diet is only short-term, the individual products can be used indefinitely, replacing one or even two meals a day.

Are they nutritious?

The products include added vitamins, minerals and other nutrients to help you meet your daily requirements. But surprisingly, they're unregulated in Australia, which means there is no one overseeing the composition of these products. 

A recent Australian analysis of eight such diets found none met all daily nutrient requirements for both men and women in all age groups.

Protein, in particular, was too low for most people, with the exception of younger, smaller women. Yet protein is likely to help you preserve muscle when you lose weight. The study authors noted that adding pure (whey) protein powder to the shakes, including two cups of low-energy vegetables, and in some cases adding some oil each day will help people meet their nutritional needs without adding too much energy.


There are possible side-effects from VLEDs, mostly resulting from the decreased energy intake – sensitivity to cold, dry skin, temporary rash, temporary hair loss, low blood pressure, dizziness, fatigue, diarrhoea, constipation, muscle cramps, irritability, gallstones and menstrual disturbances.

Medical weight loss treatments compared

Weight loss treatments Very low energy (calorie) diet (VLED) e.g. Optifast, Optislim, KicStart, Tony Ferguson Saxenda (liraglutide) Xenical (orlistat) Duromine (phentermine) Topiramate
Type of treatment Meal replacement food/drinks Appetite suppressant Reduces fat absorption from food Appetite suppressant Appetite suppressant
Cost $7.50–10.50 a day $400 a month $100 a month $100–140 a month $16 a month (plus cost of phentermine)
How you take it Replace meals with formulated low-energy food/drinks Injected twice a day Three capsules per day with meals One capsule per day In combination with phentermine
Where to get it Pharmacy OTC – but should be medically supervised Prescription only Pharmacy – behind the counter Prescription only Prescription only – off label
Possible side-effects

Sensitivity to cold, dry skin, temporary rash, temporary hair loss, low blood pressure, dizziness, fatigue, diarrhoea, constipation, muscle cramps, bad breath, irritability, menstrual disturbances.

Nausea, vomiting, diarrhoea, constipation, hypoglycaemia (especially for people taking diabetes medication), pancreatitis, gallbladder disease, kidney failure and suicidal thoughts. Wind, gut pain, runny or oily faecal discharge, headache, vitamin deficiency and kidney stones. Gastrointestinal upset, headaches, tachycardia, palpitations, insomnia, anxiety and elevated blood pressure

Paresthesia (pins and needles), dizziness, altered taste, insomnia, constipation, dry mouth, tachycardia, suicidal thoughts


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