Frequently used herbal teas during pregnancy

Herbs are frequently used as teas or infusions during pregnancy. However, there are no clinical trials and no evidence-based proof regarding their safety. They have been considered to be safe and so used for many years. Thus, their recommended consumption is to be limited to two cups per day during pregnancy¹⁰.

Commonly used herbs during pregnancy were known to be raspberry, fennel, peppermint, ginger, thyme, chamomile, sage and green tea¹⁰. Linden, peppermint-lemon, ginger have been reported to be the most commonly used herbal products in pregnancy during 1^st and 2nd trimesters in a study conducted in Turkey¹¹. Moreover, in a preliminary study conducted to evaluate the attitudes of primary care physicians towards herbal medicines used during pregnancy revealed that fennel, linden and cinnamon are the most commonly used and recommended herbal teas among pregnant women in İstanbul¹².

The red raspberry leaf is one of the most commonly used herbal tea during pregnancy primarily due to its assumed labor stimulation effect^13,14. However the need for labor stimulation or duration of labor has not been demonstrated in any study¹⁵. Like all compounds, the pregnancy risks associated with raspberry leaf have not been well studied. A 38-year-old woman with gestational diabetes mellitus using insulin, developed hypoglycemia after consuming raspberry leaf tea at 32 weeks of gestation and she had to lower her insulin dose. The relationship of her condition with raspberry leaf tea was confirmed but the extent of effect with the amount use is unknown¹⁶. In animal studies, the hypoglycemic effects of blackberry leaves have been recorded and suggested to be related to raspberry leaves^17,18. The animal and clinical studies are inadequate and unable to rule out other undesirable effects on pregnancy outcomes without any additional benefit¹⁹. It was classified in “use with caution in pregnancy” category⁶.

Peppermint is another plant used to relieve flatulence and emesis thanks to its antispasmodic , and breast milk enhancer effects. Also it acts as a sedative, and used for the treatment of respiratory and urinary tract infections^20-22 and morning sickness in pregnancy even though it is B2 Category^23,24. Inhalation of its essential oil can be used to reduce fever, relieve nausea and vomiting, and improve digestion²⁵. The antiemetic mechanism of essential oil of peppermint was based on its 5-HT3 receptor antagonistic effects²⁶. Any harmful effect of peppermint tea to mother or fetus has not been shown^6,1. However its excessive use is contraindicated in early pregnancy due to its emmenagogue effects²². On the other hand, in a randomized placebo controlled study, conducted on women with nausea and vomiting during first half of pregnancy, the nausea and vomiting decreasing effect of peppermint oil aromatherapy and placebo were found to be the same²⁷. According to safety classification of herbal medicines used during pregnancy, peppermint (15.9%) is one of the most frequently used herbal medicines classified as safe⁶.

German chamomile (Matricaria recutita) is another most commonly used herbal supplement. In a study its at least weekly usage is reported during pregnancy (7.5%)²⁸. It is used for relief of gastrointestinal irritation, insomnia, and joint irritation. However with regular use, a higher incidence of preterm labor or miscarriage has been reported²⁹. Constricted ductus arteriosus was detected in a 34-year-old woman, at 20 weeks’ gestation, who reported drinking camomile tea on a regular basis, and her condition was improved after stopping consumption of German chamomile tea. Another 32-year-old woman, at 35 weeks’ gestation, presented with ductal constriction. She reported intermittent consumption of camomile tea during pregnancy³⁰. Ductal constriction associated with camomile tea use is similar to nonsteroidal anti-inflammatory drug (NSAIDs) use which are also known to cause ductal constriction in depending on its dose, duration of its use, and gestational age. Animal studies with Camomile tea (Camellia sinensis) root extract have demonstrated its anti-inflammatory activity³¹. Chamomile was shown to have more than 120 chemical secondary metabolites, including phenolic compounds like flavonoids, sesquiterpenes and coumarins^31,32. Due to its content of coumarins, there may be risk of an additive effect when taken with warfarin²⁰. It has affinity with estrogenic receptors as coumarins, flavonoids and miscellaneous phenolic compounds. Several of them were detected to have, theoretically, more affinity than estradiol to estrogenic receptors³³. In a retrospective study where risks of herbal products on pregnancy and neonatal outcomes were investigated, the regular chamomile consumption during third trimester was found to be associated with higher risk of pre-term delivery and lower birth weight³⁴. Eventually, use of chamomile was considered to be unsafe during pregnancy with adverse perinatal outcomes.

Ginger is usually used for nausea in pregnant women especially in the first trimester³⁵. A systematic review of twenty four trials revealed that dose of 35-500 mg ginger and vitamin B6 have been shown to have identical effects against nausea and vomiting of pregnancy³⁶. For pregnant women with hyperemesis gravidarum, 1 gram per day (250 mg 4 times a day) for four days was used effectively and adverse effects were not reported. All infants were normal. Only one spontaneous abortion occurred; but a causal relationship with use of ginger was not determined³⁷. The major part of the antiemetic activity may be due to its ingredient 6-gingerol that acts directly in the gastrointestinal tract³⁸. In hyperemesis, ginger may act by stimulating the motility of the gastrointestinal tract and its absorbent property may reduce stimuli to the chemoreceptor zone. It may block the gastrointestinal reactions and the subsequent nausea feedback³⁹. The ginger also acts on 5-HT3 receptors in the ileum with serotonergic effect and anti-hydroxytryptamine activity^40,41. There are several randomized control studies showing the relieving effect of ginger in nausea and vomiting of pregnancy and it is used in different doses and durations. Ginger used in first trimester has been associated with some non–dose-dependent adverse drug reactions, such as dry mouth or worsening of nausea and dehydration^42,43, and during second and third trimesters, it has been associated with bleeding or spotting⁴⁴. Ginger use throughout pregnancy was reported to be associated with a significant prematurity and decrease in neonatal head circumference at birth³⁴. Its interaction with drugs that can be used during pregnancy such as insulin, metformin, and nifedipine has been reported⁴⁵. Risk of vaginal bleeding was reported to be associated with ginger use in pregnant women due to its possible inhibiting thromboxane synthetase activity^46,47. Interaction of ginger with fetal testosterone metabolism has been also shown^48,49. Ginger’s anti-inflammatory and analgesic effects have been demonstrated and its use in dysmenorrhea has been suggested to be due to its inhibition of cyclooxygenase enzyme⁵⁰. As there are concerns regarding its safety for women, if ginger is to be used during pregnancy, it should be in limited amounts¹⁰. The recommended dose is 1,000 mg per day for nausea and vomiting of pregnancy, not to exceed 4 g, due to its uterine stimulating effects⁵¹.

Fennel (Foeniculum vulgare), another commonly consumed plant is available in teas. Its dried ripe fruit or seeds have shown to exert estrogenic effects that may cause increase in menstruation and libido⁵². Its main constituents; anethole, dianethole and photoanethole are considered to be responsible for these estrogenic effects^53,54. Its favorable effects in hormonal disorders in women have been reported including alleviation of the symptoms of the menopause, improvement of fertility and enhancing lactation. The effects of oral fennel oil use in dysmenorrhea, premenstrual syndrome, amenorrhea and polycystic ovary syndrome have been also clinically demonstrated⁵⁵. Its anti-spasmodic effects were studied in rats and fennel essential oil was shown to reduce the frequency of contractions induced by PGE2 in isolated rat uterus⁵⁶.

The effect of fennel oil on in vitro reduction in limb bud differentiation of rat embryo demonstrated that it has toxic effects on fetal cells, without evidence of teratogenicity⁵⁷. Although it is used for years, there are still concerns regarding its potential adverse effect. Also fennel extracts were known to have human liver cytochrome P450 enzyme inhibitory activity causing potential interactions with other drugs⁵⁸. It is also commonly used during lactation period for its curative effects on infantile colic⁵⁵. As reported in the literature 12-month-old girl given two to three teaspoons of fennel tea by her mother every day for the last 6 months developed isolated premature thelarche⁵⁹. Two women who consumed herbal tea containing fennel and cumin to induce lactation during postpartum period presented with hepatotoxicity^60,2.