Then make sure first that you have researched the diet pills thoroughly, know how it will help you lose weight, what you should expect for side effects, and if there are any danger signs you should look out for that will warn you of bad reactions to the drug.
See, diet pills are not one and the same and some may work better for you and some might just make you miserable. Also, your physician should know you're taking them, as well as certain significant others. This is especially important so you can be advised if the pills would have contraindications with other medications you may be taking and so that your significant others can share the information to doctors should anything happen to you, regardless of whether it's a reaction to the pills or not.
And always, take the pills with caution. Do not skip meals in an attempt of helping these pills along. Complement it by exercising and staying active. And always, watch out for signs that your body is reacting badly to the drug, like migraines, nausea, forgetfulness, insomnia, etc.