Any time you have a question regarding what type of birth control is best for you, it is best to ask a qualified health care professional. In this case the best type of physician to see is a primary care physician
such as a family doctor
or internal medicine doctor
or an OBGYN. There are many different types of hormonal contraception. Most women today are taking a type of the combined low dose oral contraception pills. These pills have a combination of estrogen and progesterone like hormones. These newer formulations do not tend to cause weight gain as much as they used to or change in muscle mass. Some of the hormonal contraception formulations such as the Depo Provera shot can cause significant unwanted weight gain. Muscle mass should not be effected by any of these hormone medications. I think the bigger question is what your reason for taking the birth control pills. If you need them to help prevent pregnancy, then their benefits will likely outweigh any of their drawbacks. I suggest that you schedule an appointment with your primary care physician or OBGYN, whoever, you see for your feminine health. The two of you can discuss the pros and cons of each birth control method and determine which one is best for you.