Calamus Root (Acorus calamus) a.k.a Sweet Flag: Its internal use as a medicinal herbal product should only be administered by someone with experience in using this botanical. The FDA strictly prohibits the use of Calamus in food products. Because of its toxic properties, calamus should never be used during pregnancy or lactation. The topical application of any undiluted oil is not recommended. Application of perparations containing calamus oil may provoke an irritant reaction and is therefore best avoided.
Calendula (Calendula officinalis) a.k.a. Gold-bloom, Marigold, Marybud, Pot Marigold: In animal studies, calendula has shown a tightening effect on the uterus. Although no miscarriages have been reported as a result of pregnant women taking calendula, avoiding oral calendula is advised during pregnancy. I can not find any evidence that proves this effect occurs with use of calendula on the skin. I used calendula oil on my own pregnant belly, and use it on my 2 year old's eczema regularly.
California Poppy (Eschscholzia californica) a.k.a Western Poppy, Poppy, and Gold Poppy: Safety has not been established during pregnancy or nursing or for children under the age of 6. Cascara bark (Rhamnus purshiana) a.k.a. Bitter Bark, Buckthorn, California Buckthorn, Cascara Sagrada, Chittem Bark, Dogwood Bark, Purshiana Bark, Sacred Bark, Sagrada Bark, Yellow Bark: Not known to be safe for pregnant women and nursing mothers, or recommended for children under the age of 12. Contains anthraquinones; non-standardized anthraquinone-containing laxative preparations should not be taken during pregnancy or lactation since their pharmacological action is unpredictable. Although anthraquinone derivatives may be excreted in breast milk, following normal dosage their concentration is usually insufficient to affect the nursing infant. You decide if "usually' is enough to make you feel secure in passing it to your baby.
Catnip (Nepeta cataria): Mints such as catnip contain essential oils that, used internally (or extracted into a tincture) may harm the kidneys and liver; the infusion, taken in large enough quantity, may stimulate uterine contractions.
Cedar Berry (Juniperus monosperma) a.k.a. One-seed Juniper, Cherrystone Juniper, Redberry Juniper, New Mexico Cedar, West Texas Juniper, Sabina: Can be toxic when taken in large amounts. May cause contractions.
Celandine (Chelidonium majus) a.k.a. Bai Qu Cai, Chelidonii, Chelidonii Herba, Greater Celandine, Schollkraut, Tetterwort, Verruguera: Because of it's pharmacologically active constituents, including berberine and sanguinarine (a potentially toxic alkaloid), the use of celandine is best avoided while pregnant. Berberine has produced hypotensive effects in laboratory animals, exhibits uteroactivity, and has been reported to decrease the anticoagulant action of heparin in human blood in vitro.
Celery Seed: Supplements should be avoided during pregnancy/lactation due to diuretic affect and potential to deplete potassium levels. Normal culinary use is safe.
Chaparral (Larrea tridentata) a.k.a. Creosote Bush: Acute hepatitis has been associated with chaparral ingestion. In vitro uteroactivity has also been documented for chaparral. In view of the concerns regarding toxicity, it should not be ingested during pregnancy or lactation.
Chaste Tree Berry (Vitex agnus-castus) a.k.a. Chaste Berry, Monk's Berry, Vitex, Chastetree, Chinese Vitex, Gattilier, Hemp Tree, Monk's Pepper, Vitex: Hormone stimulating; not recommended during pregnancy. Some evidence suggests that low doses might increase milk production in women who are lactating, but care should be taken in this regard because this hormonal effect appears to be dose-dependent and higher doses seem to have the opposite effect.
Chervil (Anthriscus cerefolium) a.k.a. Garden Chervil, Cow Parsely, French Parsley: Safety not established during pregnancy or nursing or for children under the age of 6.
Chickweed (Stellaria media): Excessive amounts may reduce milk supply in lactating mothers.
Cinnamon: Excessive use of "solid" cinnamon (whole or ground bark) is not recommended during pregnancy because cinnamon can act as a blood thinner. Cinnamon Bark essential oil should be avoided entirely during pregnancy. Therapeutic use of cinnamon during pregnancy (i.e. to stabilize blood sugar) should be supervised by a health professional. Reasonable culinary use is considered safe.
Club Moss
Coltsfoot
Comfrey Leaf
Comfrey Root
Copal Resin
Cotton Root Bark
Couchgrass