I was taking herbs prior to my first endo visit and blood test - the herbs and their effect on my hormonal biology didn't even register in the blood work. I guess it depends on what you are taking and how much (I was using teas rather than tablets) but overall they are fairly ineffective. All the same, if you want your doctor to have a reasonable understanding of what's going on for you it might be an idea to stop them before, or at least let them know that you are using them (that's what I told mine).