Chamomile: A systematic review of adverse events

Chamomile is a well-known plant recognized for its anti-inflammatory, antidepressant, anxiolytic, and analgesic properties. The present study aimed to systematically review the adverse events associated with chamomile as reported in human studies. PubMed, Scopus, and Web of Science were searched for clinical trials, case-control studies, case reports, and case series published in English up to February 2024. The search utilized the following keywords: ((Chamomile or Camomile or " Chamomilla recutita " or " Matricaria chamomilla " or " Matricaria recutita "), and ("Side effect" or "adverse effect “or "complicat* or "complication")). Studies that involved chamomile under different scientific names (e.g., its other species such as Chamaemelum nobile ) or in combination with other herbs were excluded (PROSPERO registration number: CRD42024520053). A total of seventy-two trials and eleven case reports were included in this review. In these trials, 2,896 patients received chamomile, and 65 adverse events were reported across 10 trials. Unfortunately, the incomplete reporting of adverse events in these trials, along with the absence of any data on adverse events in 28 trials, limited the scope of our review. The most common adverse events were gastrointestinal complications and drowsiness, both of which were self-limiting and non-serious. No allergic adverse events were reported in the clinical trials; however, among the eleven case reports, six reported adverse events associated with allergic reactions to chamomile, ranging from anaphylactic reactions (in three patients) to short-lasting acute rhinitis. In conclusion, data extracted from clinical trials and published case reports suggest that chamomile is generally safe when used in controlled dosages, with self-limiting minor adverse events. However, case reports indicate that allergic reactions should be taken into consideration. Furthermore, there is insufficient data regarding its safety during pregnancy and lactation. ● Chamomile is generally safe when used in controlled dosages with self-limiting adverse events. ● The most common adverse events were gastrointestinal complications and drowsiness which were self-limiting and non-serious. ● Unfortunately, one-third of the trials did not provide any data on adverse events. ● 23% and 63% of the clinical trials did not report the purity and potency of chamomile products, respectively. ● No relationship between chamomile dosage or route of administration and adverse events was found due to heterogeneity.