Lorcaserin is what is called a serotonin agonist.  Serotonin is a chemical that is important in our brain and our guts.  It  reduces appetite and therefore reduces body weight

It appears to have fewer side effects than many of the other options although long-term safety data is not really available.

Side effects are generally mild and include a headache, upper respiratory symptoms like a congested nose, dizziness, and nausea.  And It is not to be taken during pregnancy.

The dose 10 mg once daily or twice daily

And the effects you can expect to see are about an extra weight loss of ~3-4 kg or 6-8 lbs over a year

The cost is ~$285 USD for 1-2 months, depending on if you take it once to twice a day.  It is not available in Australia.