The following list of herbs are considered unsafe to use internally during pregnancy due either to there actions on reproductive organs or because of certain naturally-occurring substances found in them. Herbs listed as anthraquinone laxatives should be avoided due to there stimulating effects on smooth muscle which can include uterine tissue causing a potential miscarriage. Herbs listed as uterine stimulants should be avoided for the same reason.
Herbs listed as abortifacients have a strong potential to cause a miscarriage.
Herbs listed as emmenagogues help promote and regulate mentruation, something to avoid in pregnancy. The herbs listed as having alkaloids, bitter principles or essential oils in them should not be used because of the effects these principles have on functions in the body of the mother or the fetus. Culinary herbs like oregano and thyme are safe in the small amounts used in cooking but not in the larger doses used for teas or tinctures. If you are unsure about an herb or what a safe amount is, it is best to avoid the herb or seek the advice of a herbal practitioner or naturopath. Dictionary of Modern Herbalism, Mills, Simon Y.,Healing Arts Press, 1988.