Drug info

Weight-loss medicines

Weight management medicine Mostly prescription only

The approved weight-loss medicines side by side: how much weight people actually lost in the trials, what they cost your stomach, and what happens when you stop. Spoiler: the newer injections lead, and none of them is a course you finish.

At a glance

For
Adults with obesity (BMI 30 or more), or BMI 27 or more with a weight-related condition, alongside diet and activity
Works
Average loss in the main trials: tirzepatide 15–21%, semaglutide about 15%, phentermine/topiramate about 9% more than dummy treatment, liraglutide 8%, naltrexone/bupropion about 6%, orlistat a few kilograms. Dummy treatment: about 1–3%
Cost
None are on the PBS for weight loss (October 2026). Wegovy is being reconsidered for some people with heart disease and obesity
Kicks in
Appetite changes within weeks; most weight loss over 6–18 months
Taken for
Long term for most. Phentermine is approved only for short courses (up to 3 months)
Watch for
Nausea and gut upsets (injections), racing heart and poor sleep (phentermine), oily leakage (orlistat)

If it’s sold with a before-and-after photo and a countdown timer, it isn’t on this list for a reason.

Brand names

How it works

Used for

Compared

Weight figures are average loss in the main trial, on the medicine versus a dummy treatment. Both groups had diet and activity advice, so the medicine’s effect is on top of lifestyle changes.

  1. Weekly injectionTirzepatide (Mounjaro)
    How it works
    Copies two gut hormones (GIP and GLP-1)
    How taken
    Weekly injection, dose stepped up every 4 weeks
    Weight loss
    SURMOUNT-1: 15.0–20.9% (by dose) vs 3.1% over 72 weeks
    Common side effects
    Nausea, diarrhoea, vomiting, constipation, less appetite
    Not for
    Pregnancy; medullary thyroid cancer or MEN2. Can make the pill less reliable
    When stopped
    SURMOUNT-4: people switched to dummy injections regained 14% of their weight over the next year; those who continued lost another 5.5%
  2. Weekly injectionSemaglutide 2.4 mg (Wegovy)
    How it works
    Copies a gut hormone (GLP-1)
    How taken
    Weekly injection, dose stepped up every 4 weeks
    Weight loss
    STEP 1: 14.9% vs 2.4% over 68 weeks
    Common side effects
    Nausea, diarrhoea, vomiting, constipation, gallstones
    Not for
    Pregnancy; medullary thyroid cancer or MEN2
    When stopped
    STEP 1 extension: about two-thirds of the lost weight came back within a year
  3. Daily injectionLiraglutide 3 mg (generics)
    How it works
    Copies a gut hormone (GLP-1)
    How taken
    Daily injection
    Weight loss
    SCALE: 8.0% vs 2.6% over 56 weeks
    Common side effects
    Nausea, diarrhoea, constipation, vomiting
    Not for
    Pregnancy; medullary thyroid cancer or MEN2
    When stopped
    Weight tends to return, as with the weekly versions
  4. Daily capsulePhentermine (Duromine)
    How it works
    Stimulant appetite suppressant
    How taken
    One capsule in the morning (not at night: it keeps you awake)
    Weight loss
    Approved only for short courses, so long-term trial data are thin
    Common side effects
    Racing heart, raised blood pressure, poor sleep, restlessness, dry mouth
    Not for
    Heart or blood vessel disease, moderate to severe high blood pressure, overactive thyroid, glaucoma, past drug or alcohol misuse, agitation or some mental health conditions
    When stopped
    Courses are limited to 3 months, then reviewed
  5. Not approved in AustraliaPhentermine with topiramate (Qsymia)
    How it works
    Stimulant plus an anti-seizure medicine that also reduces appetite
    How taken
    Daily capsule (US). In Australia, sometimes as two separate off-label scripts
    Weight loss
    EQUIP and CONQUER: about 9% more than dummy treatment over 56 weeks at the top dose
    Common side effects
    Tingling, dry mouth, constipation, taste change, mood or concentration problems
    Not for
    Pregnancy (topiramate causes birth defects, so reliable contraception is essential), glaucoma, overactive thyroid, heart disease
    When stopped
    Weight tends to return
  6. TabletsNaltrexone with bupropion (Contrave)
    How it works
    Acts on the brain’s appetite and reward pathways
    How taken
    Tablets, built up over 4 weeks to 2 tablets twice a day
    Weight loss
    COR-I: about 6.1 kg vs 1.4 kg (roughly 6% vs 1%) over 56 weeks
    Common side effects
    Nausea, constipation, vomiting, headache, dizziness, dry mouth
    Not for
    Seizures, anyone taking opioids (it blocks them), uncontrolled blood pressure, eating disorders, bipolar disorder, pregnancy
    When stopped
    Stopped at 16 weeks if less than 5% of body weight has been lost
  7. Capsule with mealsOrlistat (Xenical)
    How it works
    Blocks about a third of dietary fat from being absorbed
    How taken
    Capsule with each main meal that contains fat
    Weight loss
    XENDOS: 5.8 kg vs 3.0 kg over 4 years, with 37% fewer new cases of diabetes
    Common side effects
    Oily spotting, wind with discharge, urgent or fatty stools, worse after fatty meals
    Not for
    Long-term gut absorption problems, bile flow problems, pregnancy
    When stopped
    Effects stop when the capsules do

Coming soon (not approved in Australia)

  1. Not approved in AustraliaSemaglutide 25 mg tablet (Wegovy pill)
    Status
    Approved in the US in December 2025
    Weight loss
    OASIS 4: 16.6% vs 2.7% over 64 weeks, in people who kept taking it
  2. Not approved in AustraliaOrforglipron (Foundayo)
    Status
    Daily pill, no food or water timing rules. Approved in the US in April 2026; submitted to the TGA
    Weight loss
    ATTAIN-1: up to 11.2% vs 2.1% over 72 weeks
  3. Not approved anywhereCagriSema (cagrilintide with semaglutide)
    Status
    Weekly injection. US decision expected late 2026
    Weight loss
    REDEFINE 1: 20.4% vs 3.0% over 68 weeks
  4. Not approved anywhereRetatrutide
    Status
    Weekly injection acting on three hormones. Still in trials
    Weight loss
    TRIUMPH-1: 19.0–28.3% (by dose) over 80 weeks

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Side effects

Get help urgently if

Good to know

Common questions

Which weight-loss medicine works best?

On average, tirzepatide, then semaglutide. In a head-to-head trial, people lost 20.2% of their weight on tirzepatide versus 13.7% on semaglutide over 72 weeks. Results vary a lot from person to person.

Do I have to take weight-loss medicine forever?

For most people, the weight comes back after stopping. In trials, most of the lost weight returned within a year of stopping semaglutide or tirzepatide. They work more like blood pressure medicine than a course of antibiotics.

Are weight-loss injections on the PBS?

Not for weight loss, as of October 2026. Ozempic is PBS-subsidised for type 2 diabetes only. Wegovy is being reconsidered for some people with heart disease and obesity.

Do weight-loss supplements work?

Not in good-quality trials. Garcinia, green tea extract, raspberry ketone and similar products show little or no effect, and some have been linked to liver damage.

Information only. Not a recommendation or endorsement of any product. Whether a medicine suits you depends on your health and other medicines, so talk to your doctor or pharmacist. In an emergency, call 000 (Australia) or your local emergency number. From a mobile, 112 works in most countries.

More information

Reviewed 31 October 2026.

Related

maladywise.com/medicines/weight-loss-medicines/