Phentermine is one of the most commonly prescribed weight loss drugs.  That is its drug name, and Duromine and Adipex are two of its brand names

It is in a class of drugs called SYMPATHOMIMETIC DRUGS.  These drugs stimulate the release of noradrenaline or norepinephrine, which makes you feel full from food earlier, hence you eat less and you lose weight.

There are a range of potential side effects with this class of drugs that you should be aware of –

It is contraindicated in patients with forms of heart disease, high blood pressure, an overactive thyroid gland, or in patients with a history of drug abuse

Its potential side effects include psychiatric concerns like depression and anxiety, cognitive concerns like the disturbance in attention, increased heart rate, increased blood pressure, sleep problems like insomnia, dry mouth, and constipation

The exact likelihood of these occurring you will have to ask your pharmacist or doctor

It was previously only approved for the short-term use, up to 12 weeks, but studies have shown that the addiction potential of long-term phentermine use is low, and there is minimal evidence that long-term phentermine monotherapy is associated with serious side effects

The benefit you would expect to see is on average 5-6kg or 10-12 lbs extra in ~3 months on top of doing the lifestyle changes

The cost is about $100-$130 AUD a month if you live in Australia or $10-20 USD a month if you live in the USA