Dong Quai/Dang Gui/Angelica Root (Angelica sinensis): There is some debate between Western physicians and the Chinese concerning Dong Quai. Generally, most Western physicians recommend pregnant and lactating women avoid it because it is said to help relax the smooth muscles throughout the body, including the uterus. According to the Mayo Clinic, Dong Quai is not recommended during pregnancy due to possible hormonal and anticoagulant/anti-platelet properties. It then goes on to say that animal studies noted conflicting effects on the uterus, with reports of both stimulation and relaxation (http://www.mayoclinic.com/health/dong-quai/NS_patient-Dongquai). Practitioners of TCM would probably say that is a bunch of nonsense. I've found nothing but conflicting information.
Elecampane
Ephedra
Eleuthero Root
Epimedium (Horny Goat Weed): Western medicine recommends limiting its use during pregnancy/lactation because of lack of clinical trial data. It's a common Western "better safe than sorry" rule.
“Essiac”
Eyebright
False Unicorn
Fenugreek: medicinal doses are considered a uterine stimulant; however, is SAFE for breasteeding and may drastically improve milk supply; may cause characteristic "maple syrup" odor in breast milk (and mother).
Feverfew: A uterine stimulant which may cause premature contractions. I can't find any reliable information indicating that the topical, diluted amount of Feverfew (Chrysanthemum Parthenium) extract in facial moisturizer is harmful to a developing embryo, fetus or breastfed child.
Fo-Ti Root
Forsythia Fruit
Frankincense
Fringe Tree Bark
Fumitory
Galangal Root
Ginger (in large amounts): Because ginger has been scientifically linked to embryotoxic effects in laboratory rats (Vutyavanich T, et al.. Ginger for nausea and vomiting in pregnancy: randomized, double-masked, placebo-controlled trial. Obstet Gynecol. 2001 Apr;97(4):577-82.), pregnant women are advised take less than two grams per day for no more than five days at a time, waiting at least one week before resuming. The editor of the German Commission E Monographs notes that there is no evidence that ginger causes any harm to a lactating mother or breastfed child. I have found no evidence to support that normal culinary amounts of ginger have any adverse side effects, either.
Ginseng
Goldenrod
Goldenseal: A uterine stimulant which may lead to premature contractions but is considered safe during childbirth.
Gotu Kola
Gravel Root
Guarana: The safety of guarana in pregnant or nursing women has not been established, which means (of course) that it should be used with intelligence and caution. Guarana is a "natural source" of caffeine (Guarnine), containing two to three times the amount of caffeine as coffee. The amount of caffeine doesn't have to be listed on guarana drinks, either, so it's often impossible to know how much you (and your baby) are getting.
Gymnema Leaf