Herbal medicines in 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”​[1]​. 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​[2]​.

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​[3]​. The authorised herbal medicine products can be found on the MHRA website​[3]​. 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​[4]​.

A WHO survey published in 2019 recorded that 88% of WHO member states (170) have reported the use of traditional and complementary medicine​[5]​. In another report, it was estimated that 65–85% of the global population used herbal medicines as their primary form of healthcare​[6]​. 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​[20]​. 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​[21]​).

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​[22]​. 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​[22]​.

Pregnant women may perceive herbal medicines as natural and safe alternatives to conventional medicines​[23]​. 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​[23]​. 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​[26]​. 

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​[23]​. Therefore, it may be difficult to assess the safety aspect of the different preparations for a herbal medicine​[23]​. 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​[23]​. This should be considered when determining the safety of herbal medicines as the rate of drug absorption may differ depending on the formulation used​[23]​.

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​[7]​. The commonly reported indications during pregnancy worldwide are​[7]​:

• Morning sickness;
• Cold and flu;
• Pain (gastralgia and other types of pain);
• Anxiety;
• Stress;
• Gastrointestinal disorders, such as constipation and flatulence;
• Oedema;
• Urinary tract infection;
• Labour preparation, facilitation and induction;
• Milk production and secretion;
• Foetal health promotion;
• Anaemia.

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​[6]​. 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.

Herb–drug interactions

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)​[48]​. Of these respondents, 45% used at least one herbal medicine and a potential herb–drug interaction was identified in 13% (see Table​[48]​).

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​[23]​. 

Women who wish to take herbal products medicinally during pregnancy should consult a healthcare professional, and the risks and benefits should be carefully assessed​[23]​.

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​[23]​. 

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​[23]​. 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​[23]​. 

If herbal medicines are required as essential treatments, they should be obtained from a reputable source and taken at the recommended dosage​[23]​. 

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​[57]​. 

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​[58]​. 

Other resources are available to check the safety of herbal medicines use in pregnancy, such as herbal medicines textbooks and websites​[4,28,49]​.

Summary

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.