if a woman wants to conceive & needs to lose some weight can she take weight loss tablets before that or there is bad side effects & for how long she should stop using them?

Weight loss tablets may work in the short run, but you definitely should not take them while you are pregnant. Since they don't change your eating habits, once you go off them, you will put all the weight back on that you had lost, plus some extra. Instead of going that route, try changing your eating habits to a diet that will be okay to continue during pregnancy, like the South Beach Diet. Also, start exercising now, because it will really help you lose weight, as well as stay toned during the pregnancy. Good luck!

Weight loss tablets are definitely off limits during a pregnancy! Most of them are high in caffeine and ephedrine, which can cause all kinds of issues with the proper development of your unborn child.
Proper dieting and regular exercise are your best way towards keeping yourself healthy during your pregnancy. I suggest Nutrisystem for people without any education or experience with nutrition, and because they will help you to build a diet that is perfect for your individual needs...

those are risky somewhat if taken without physician's advice..