Is it bad to take phentermine pills to lose weight?

No: As long as you are talking it under supervision of a physician and you are using it in conjunction with a proper diet and exercise regimen. Diet and exercise is the key.

Risks of phentermine: We worry about cardiovascular events like heart attack with phentermine; small risk, but... There's no risk of that happening with good diet changes. It's a stimulant so i'd especially avoid in those with hypertension. Furthermore, the weight loss is temporary- it's almost gaurenteed to come back once stopped and if you haven't made any lifestyle changes.

Phentermine: Yes. It's bad. Doctor supervisedor not, the side effects are one thing. Serious side effects like pulmonary ones are yet another. And in most cases, once pills are stopped, if there is/was weight loss, the weight is gained back. So diet, exercise and lifestyle modifications which can be obtained with a diet coach are more important.