After reading this article, you should be able to:
- Understand the prevalence of herbal medicine use during pregnancy;
- Identify the common indications and most frequently used herbal medicines during pregnancy globally;
- Explain the potential for herb–drug interactions;
- Understand how the limited information available can guide us on the use of herbal medicines commonly used during pregnancy.
The World Health Organization (WHO) defines herbal medicines as “herbs, herbal materials, herbal preparations and finished herbal products that contain as active ingredients, parts of plants, other plant materials or combinations”. Herbal medicines span the spectrum from home-brewed teas prepared from collected leaves and herbs, to products with official approved status granted by national regulating authorities.
In the UK, herbal medicines are registered via the Traditional Herbal Registration (THR) Scheme under the Medicines and Healthcare products Regulatory Agency (MHRA), which requires herbal medicines to meet the specific and appropriate standards of safety and quality. The authorised herbal medicine products can be found on the MHRA website. Information on the safety of herbal medicines during pregnancy for more than 150 herbal products can be found in herbal monographs on the European Medicines Agency’s website.
A WHO survey published in 2019 recorded that 88% of WHO member states (170) have reported the use of traditional and complementary medicine. In another report, it was estimated that 65–85% of the global population used herbal medicines as their primary form of healthcare. Women have been identified as the main users of herbal medicines, and this widespread use extends into pregnancy[7,8].
With reference to several studies, it was reported that 10–74% of pregnant women in Africa, Australia, the United States, Europe and the UK use herbal medicines[9–19]. Prevalence depends on geographic location, ethnicity, cultural traditions and social status. In the UK, approximately 40% of pregnant women use herbal medicines to treat pregnancy related problems or improve pregnancy outcomes[12,13]. The findings from eight cross-sectional studies (2,729 participants) conducted across seven Asian countries (data up to 2016) found 1,283 women (47% of the sample) reported that they had used one or more herbal medicine during pregnancy (See Figure 1).
Another cohort study conducted in South West England found that 27% (n=3,774) of women had used complementary or alternative medicine at least once during pregnancy, with use increasing from 6% in the first trimester to 12% in the second, and to 26% in the third. The use of complementary medicines also increased with the age of the mother, with the results showing that 44% of mothers aged above 35 years used complementary medicines, compared with 15% of respondents aged 24 years or younger.
Pregnant women may perceive herbal medicines as natural and safe alternatives to conventional medicines. However, some plants have toxic constituents and many have constituents with pharmacological activity, such as stimulation of uterine muscle and induction of labour (e.g. black cohosh)[24,25]. Contamination with substances such as pesticides, conventional medicines or heavy metals (e.g. lead) also has to be taken into account. For example, in 2012 there were reports of six cases of lead poisoning in New York resulting from the use of imported Ayurvedic herbal medicine by pregnant women.
Herbal medicine preparations often vary with respect to the concentration and origin of their constituent herbs[23,27]. Many modern herbal preparations are available as highly concentrated extracts and their effects could differ substantially from those of more traditional preparations, such as tea made from the herb’s leaves. Therefore, it may be difficult to assess the safety aspect of the different preparations for a herbal medicine. As with conventional drugs, there may be a number of formulations available — e.g. capsule, tinctures, cream, dried leaves — for a herbal medicine with different methods of administration. This should be considered when determining the safety of herbal medicines as the rate of drug absorption may differ depending on the formulation used.
Indications for use of herbal medicines during pregnancy
The traditional indications for the use of herbal medicines during pregnancy can be related to the treatment of pregnancy-related problems or to improve the well-being of the mother or unborn child. The commonly reported indications during pregnancy worldwide are:
- Morning sickness;
- Cold and flu;
- Pain (gastralgia and other types of pain);
- Gastrointestinal disorders, such as constipation and flatulence;
- Urinary tract infection;
- Labour preparation, facilitation and induction;
- Milk production and secretion;
- Foetal health promotion;
Pharmacological activity of different herbal medicines during pregnancy
The data from scientific studies into the effects of herbal medicines in pregnancy, and the literature reporting relating to the outcome of pregnancies during which herbal medicines were used, are relatively limited. In view of this, the use of herbal medicines during pregnancy is not recommended. Nevertheless, there is a large and growing number of pregnant women using herbal medicines and it is important for pharmacists to be able to communicate the available evidence to patients and to be able to work from first principles when considering why herbal medicines are not generally recommended during pregnancy. The widespread use of herbal medicines has allowed for a number of cross-sectional studies to be conducted, which has produced some useful information to inform recommendations regarding some commonly used herbal medicines during pregnancy.
The boxes below provide examples of five herbal medicines, illustrating their indications for use and the supporting information underpinning recommendations around their use during pregnancy. Please note that this is a selection of examples to illustrate the limited nature of the information available and not an exhaustive list of herbal medicines.
Box 1: Blue cohosh
When used orally, blue cohosh is a uterine stimulant and can induce labour. Several blue cohosh constituents, such as anagyrine and N-methylcytisine, are potentially teratogenic and might cause congenital malformations in newborns.
The potential foetal and newborn toxicity appears to outweigh any medical benefit. The use of blue cohosh should be avoided[28–33].
Box 2: Borage (Borage oil)
Borage is unsafe to be used in pregnancy when taken orally. This herbal medicine contains hepatotoxic pyrrolizidine alkaloids when it is used orally.
This herbal medicine should be avoided during pregnancy owing to possible teratogenic effects. It has a prostaglandin E agonist action which can have labour inducing effects[30,33–35].
Box 3: Dong quai
One observational research study has found that intake of An-Tai-Yin, an herbal combination product containing dong quai and parsley, during the first trimester is associated with an increased risk of congenital malformations of the musculoskeletal system, connective tissue and eyes.
Dong quai has uterine stimulant and relaxant effects and hence can potentially increase the risk of miscarriage. Dong quai is not recommended to be used during pregnancy[36–39].
Box 4: Ginger (root)
Between 50–80% of women experience nausea during pregnancy. A Cochrane review concluded that the use of ginger may be helpful to women, but the evidence of effectiveness was limited and not consistent. The current National Institute for Health and Care Excellence guidance on antenatal care mentions that ginger appears to be an effective intervention in reducing nausea and vomiting symptoms in early pregnancy.
According to information produced by the UK Teratology Information Service, results from three cohort studies, one case-control study and several small clinical trials showed no increase in the incidence of adverse pregnancy outcomes, including congenital malformations, when ginger was used during pregnancy. Despite this, since only small numbers of pregnant women have been exposed to ginger in studies, the risk of adverse effects cannot be completely ruled out.
During pregnancy, it has been suggested that women do not take doses of ginger exceeding 1g/day for the indication of nausea and vomiting.
Ginger has limited potential to stimulate uterine smooth muscle. Despite this theoretical concern, the risk posed by ginger to the foetus is considered to be low, particularly when it is used at the doses found in foods, such as ginger biscuits[35,40–43].
Box 5: St John’s wort
St John’s wort induces CYP 3A4 and P-glycoprotein and therefore has the potential to interact with many drugs, including those conventional drugs taken by the pregnant women.
Preliminary population research has found that taking St. John’s wort while pregnant is associated with offspring that develop neural tube, urinary and cardiovascular malformation. Subgroup analyses suggest that these risks may be higher when taking St. John’s wort during the first trimester when compared with the second or third trimester. However, more research is needed to confirm these findings.
Animal-model research also shows that constituents of St. John’s wort might have teratogenic effects. Until more safety data is released, St. John’s wort should not be taken during pregnancy.
In the clinical guidelines on the management of depression in adults, NICE advises against prescribing or advising the use of St John’s wort; however, unintentional exposure to St John’s wort during early pregnancy may occur.
In view of the lack of toxicity data, use of this herbal medicine during pregnancy is not recommended[28,44–47].
A further concern is herb–drug interactions between herbal medicines and any conventional medicine(s) being taken by a pregnant woman, which may potentially harm the mother and/or the foetus[8,48]. The number of women needing to take conventional medicines during pregnancy is increasing[49–52]. It is important that pharmacists are aware of any potentially harmful herb–drug interactions and educate patients around the risks.
In a survey conducted in Scotland completed by 889 women during early pregnancy or immediately after delivery, 45% of women reported using prescription medicines (excluding vitamins). Of these respondents, 45% used at least one herbal medicine and a potential herb–drug interaction was identified in 13% (see Table).
Practical advice in relation to the use of herbal medicines during pregnancy
Herbal medicines should generally be avoided during pregnancy as most herbal medicines have not undergone rigorous clinical testing before being made available. There might be little or nothing known about their therapeutic and adverse effects during pregnancy, as well as any drug–herbs interactions.
Women who wish to take herbal products medicinally during pregnancy should consult a healthcare professional, and the risks and benefits should be carefully assessed.
Healthcare professionals should consider the reason(s) why a woman wishes to take herbal medicine. Undiagnosed illness that remains untreated by conventional methods might result in maternal and foetal toxicity.
It is important for the healthcare professional to take a complete drug history, including the use of herbal medicines from the pregnant women both in the hospital and primary care setting[53,54].
Herbal medicines are not safe alternatives to conventional medicines during pregnancy. They might possess toxic constituents, contaminants and they may vary with regard to the concentration and source of their constituent herbs. Some herbal medicines may contain contaminants such as heavy metals, pesticides or conventional medicines, which may be harmful to the foetus. It is important to counsel the mothers regarding this when they consider taking herbal medicines.
There is the potential for herbal medicines to interact with each other and with any conventional medicines being taken[23,48]. They can also pose problems in the peri-operative setting because of the drug interactions between the herbal medicine and anaesthesia; some are therefore recommended to stop two weeks prior to any surgery[24,55]. Ginseng, garlic and ginkgo for example may impair coagulation.
If herbal medicines are required as essential treatments, they should be obtained from a reputable source and taken at the recommended dosage.
Herbs that are commonly used in cooking would not be expected to be harmful during pregnancy in the quantities usually contained in foods; however, in large doses or concentrated forms, culinary herbs such as sage and garlic may be associated with risks in pregnancy[23,56].
Suspected adverse reactions (including congenital abnormalities) associated with maternal use of herbal medicines should be reported to the MHRA and the Commission on Human Medicines (CHM) via the yellow card reporting system.
Healthcare professionals can contact the UK Teratology Information Service (UKTIS) for assistance in making a patient-specific risk assessment when exposure to herbal medicines has occurred.
Other resources are available to check the safety of herbal medicines use in pregnancy, such as herbal medicines textbooks and websites[4,28,49].
With reference to different studies, the number of women who use herbal medicines during pregnancy has been increasing globally. This article outlined some of the main factors healthcare professionals need to consider when managing patients who choose to take herbal medicines.
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