Personally and from experience, I would suggest not to nor recommend using diet pills.
Diet and exercise is the best way to lose and maintain weight. Because once you lose the weight, you probably will have to maintain the weight. So you need to find a diet best for you, that works for you, that you can live with for the rest of your life. Diet pills are only temporary, plus can damage organs, especially heart.
I have read where thyroid hormone meds T-4 to keep the thyroid at suppressed levels might shrink goiters/nodules, but there is still a debate out about the scientific aspect of this theory - Most medicals believe this theory does not work.
Good Luck and Good Luck with the diet - you can do it, and, you can do it without diet pills.
Have you had your blood sugar checked?
You may be pre-diabetic or diabetic. Either way, I would suggest a "diet" in accordance with the American Diabetic Association's diet which is 5 small meals a day and no more than about 15 grams of carbs per meal. Snack on fruits, cheese, etc. (South Beach is close to the ADA's diet.)
Often times thyroid problems go hand-in-hand with glucose problems. Even if you don't have glucose problems, the ADA diet is very healthy.
Good luck!!