It is important to declare all medications over the counter and prescription at your first doctors appointment.
I got to thinking about this because of these TV commercials about the prescription drugs that cause birth defects. Of course they don't know they're dangerous to a baby until after so many cases of problems occur so you have to be careful. I've seen these ads for Zoloft and Topamax most recently.
Luckily I don't take much medication, but I do have athsma and the daily medication I was on originally was not a good one to use while pregnant so when I told my allergist that I was trying to get pregnant he switched me from Advair to Pulmicort right away. I'm glad I told him though I'm not sure why I did I don't recall him asking.
Medications are made to mess with your body so you know that if they can have a significant effect on you they will have an effect on the baby so you want to make sure that you are taking medications that are safe.
Even herbal supplements can cause complications with pregnancy. You wouldn't think something natural would cause problems but they sure can. Here's a list from the American College of Nurse Midwives:
Alkaloid Containing Plants: (May constrict blood vessels, cause increase in blood pressure.)
Bitters: (May cause fetal defects and/or miscarriage.)
Diuretics: (Encourage water loss)
Uva-Ursi (large doses)
Emmenagogues: (Induces loss of uterine lining -- may cause miscarriage.)
Basil, oregano, marjoram (Okay in "normal" amounts, used as spices)
Black Cohosh (last six weeks okay)
Blue Cohosh (last six weeks okay)
Ginger (okay in "normal" amounts)
Motherwort (OK in small doses)
Squaw Vine (small amounts okay)
Some of these herbs may be safe when used by skilled practitioner in appropriate doses and some may be used in late pregnancy to help prepare for birth. Make sure you know what you're doing before using any supplements during pregnancy!
Always talk to your doctor about medications and supplements and only use prenatal vitamins prescribed by your doctor.