An Overview of Systematic Reviews of Chinese Herbal Medicine in the Treatment of Migraines

Background: In the past, systematic reviews (SRs) and meta-analyses (MAs) have been used to assess the efficacy of Chinese herbal medicine (CHM) in the treatment of migraines. However, robust conclusions have not yet been determined because of variations in the methodological and evidence quality of these SRs/MAs.

Objectives: We aimed to assess the methodological and reporting quality of SRs/MAs and evaluate the available evidence of the efficacy of CHM treatment of migraines.

Methods: We searched eight electronic databases from inception until 10 January 2022, without language restrictions. Two researchers were independently responsible for study screening and data extraction. The methodological and reporting quality of SRs/MAs were assessed using A Measurement Tool to Assess Systematic Reviews (AMSTAR) 2 and Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). The evidence quality of included SRs/MAs was evaluated by Grading of Recommendations Assessment, Development and Evaluation (GRADE). In addition, a descriptive analysis of the included SRs/MAs was included.

Results: Sixteen SRs/MAs, including 69 outcomes, were finally included in this overview. Data synthesis of the included SRs/MAs outcomes showed that CHM plus Western medicine (WM) was beneficial in the improvement of migraines. In comparison, there was conflicting evidence for the effectiveness of CHM used alone. CHM was better than WM in improving responder rate and acute medication usage and was superior to placebo in improving migraine days, responder rate, and migraine duration. However, there was insufficient evidence to verify the effectiveness of CHM for migraine treatment regarding pain severity and migraine frequency. All the included SRs/MAs showed extremely low methodological and reporting quality. The results of the GRADE system indicated that the quality of most of the pooled evidence was very low.

Conclusions: CHM may be beneficial in improving migraines and can be used as a complementary therapy. However, we should treat the conclusions of the evaluated SRs/MAs cautiously because of the low quality of evidence. Future SRs/MAs should focus on improving methodological and reporting quality. High-quality randomized controlled trials (RCTs) are needed to provide strong evidence for the efficacy of CHM treatment of migraines.

1 Introduction

A migraine is typically a recurrent moderate-to-severe headache (Burch, 2019) and is one of the most prevalent and disabling disorders in the world. In the Global Burden of Disease Study 2016, migraines accounted for 45.1 million years of life lived with disability globally (GBD 2016 Neurology Collaborators, 2018; Dodick, 2018).

A recent study showed that migraines might be a risk factor for structural changes in the brain (Bashir et al., 2013). Drug therapy for migraines includes acute and preventive treatment. Acute treatment relieves the pain of a headache attack, and first-line treatments include non-steroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen, diclofenac, aspirin, and naproxen), triptans, and ergot derivatives (Orr et al., 2015; Hsu et al., 2017; American Headache Society, 2018; Kouremenos et al., 2019; Steiner et al., 2019). Preventive therapy is available for patients suffering from mild to moderate migraines. The most widely accepted first-line treatments include anti-epileptic drugs (such as divalproex sodium, valproate sodium, and topiramate) and beta-blockers (such as metoprolol, propranolol, and timolol) (Huang et al., 2017; American Headache Society, 2018; Kouremenos et al., 2019; Kowacs et al., 2019). Many studies have validated the effectiveness of these recommended treatments. However, poor tolerability, varying degrees of adverse reactions, and contraindications limit the use of these treatments (Dodick, 2018; Burch, 2019; Steiner et al., 2019).

Chinese herbal medicine (CHM) is a popular treatment in complementary and alternative medicine (CAM), typically taking the form of herbal formulations consisting of a mixture of herbs. The clinical application of CHM is based on the syndrome type of the disease. CHM has been extensively employed for migraine treatment in China. The route of administration to treat migraines is mainly oral, and common dosage forms include decoctions, pills, powders, pastes, tablets, and granule formulations. CHM can treat migraines through multiple components, targets, and pathways, which may be related to four aspects as follows. First, by adjusting the level of neurotransmitters, such as regulating 5-hydroxytryptamine (5-HT) content and the expression of its receptor, increasing norepinephrine (NE) and dopamine (DA) release in the central catecholamine system, and regulating the release of human beta-endorphin (β-EP). Second, by regulating the levels of inflammatory factors, such as calcitonin gene-related peptide (CGRP), substance P (SP), homocysteine (Hcy), and interleukin (IL), to reduce neurogenic inflammation. Third, by boosting vasomotion to enhance cerebral blood flow, followed by improved hemorheology. Finally, by enhancing pain thresholds to alleviate or avoid headaches (Hou et al., 2017; Huang et al., 2020; Li et al., 2020; Chen et al., 2021; Wen et al., 2021). In the past, many evidence-based systematic reviews (SRs) or meta-analyses (MAs) have been performed to evaluate the use of CHM to treat migraines. Nevertheless, the quality of these SRs/MAs has not yet been assessed, and their conclusions were inconsistent. Consequently, the guidance for clinical users and physicians was limited.

Overviews are a relatively novel approach to evaluate the research methods and evidence from related SRs (Hunt et al., 2018). A Measurement Tool to Assess Systematic Reviews (AMSTAR) 2 and Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) are usually employed to evaluate the methodological and reporting quality of SRs and MAs, respectively. Grading of Recommendations Assessment, Development and Evaluation (GRADE) is used to evaluate the quality of pooled evidence in SRs/MAs, reflecting the methodological quality of the original randomized controlled trials (RCTs) included in SRs/MAs. Consequently, overviews can present the overall quality of evidence relating to the use of CHM to treat migraines as well as the shortcomings of available research studies, enhancing the usefulness of existing evidence (Tian, 2019). In the present study, we performed an overview to critically evaluate the methodological and reporting quality of SRs/MAs relating to the use of CHM to treat migraines; we also assessed the current evidence for the use of CHM in treating migraines.

2 Methods

2.1 Search Strategy

Two investigators (GF and XF) independently searched the PubMed, Embase, Cochrane Library, Web of Science, China National Knowledge Infrastructure, Wan Fang Database of China, VIP Journals, and China Biomedical Literature databases from inception until 10 January 2022, without language restrictions. The search terms used were: “Migraine”; “Migraine Disorders”; “Migraine Headache”; “Acute Confusional Migraine”; “Migraine Variant”; “Sick Headache”; “Migraine Variant”; “Status Hemicranicus”; “Medicine, Chinese Traditional”; “Traditional Chinese Medicine”; “Herbal Medicine”; “Medicine, Traditional”; “Meta-Analysis”; “Data Pooling”; “Clinical Trial Overview”; and “Systematic Review”. The search strategy was adjusted according to the characteristics of each database. The details of the search strategy are shown in Table 1.

TABLE 1

TABLE 1. The search strategy.

2.2 Eligibility Criteria

Each study met the following criteria:

• Type of study: SR/MA of RCTs related to the effectiveness of CHM for treating migraine.

• Type of participant: participants diagnosed with migraine by any internationally recognized classification, such as the diagnostic criteria for headache disorders, cranial neuralgias, and facial pain (ICHD-1) (Headache Classification Committee of the International Headache Society [IHS], 1988); The International Classification of Headache Disorders, 2nd edition (ICHD-2) (Headache Classification Committee of the International Headache Society [IHS], 2004); and The International Classification of Headache Disorders, 3rd edition (ICHD-3) (Headache Classification Committee of the International Headache Society [IHS], 2013).

• Type of intervention: the treatment group was treated with CHM formulas alone, combined with Western medicine, (WM) or placebo-controlled (PC), regardless of the drug form, dose, frequency, and duration of treatment. The comparison group was treated with WM or PC.

• Type of outcome: we referred to migraine clinical trial guidelines (Tassorelli et al., 2018) to develop outcome indicators, including migraine days, acute medication usage, responder rate, pain intensity (rated by measurement tools: visual analog scales [VAS] and/or numerical rating scales [NRS]), migraine frequency, migraine duration, adverse events, depression and anxiety, the patient’s reported outcome measures, and quality of life.

We used the following exclusion criteria: (1) the study was repeatedly published; (2) SRs/MAs with incomplete data or the evidence was not synthesized; (3) network meta-review; (4) the comparison group used CHM therapy; (5) the treatment group was treated with a single herbal medicine or herbal medicine ingredient.

2.3 Study Selection and Data Collection

Two researchers (GF and XF) were independently responsible for study screening and data extraction. Disagreements were resolved through discussion with a third researcher (WS). To preliminarily exclude the literature that was not relevant to the purpose of the study, initial screening was performed by reading titles and abstracts. We then carefully read the full text of papers that passed this screening to determine the final inclusion of studies. A data extraction form was designed and used to collect basic information about each study, including author information, year of publication, intervention measures, outcome indicators, study type, and conclusions.

2.4 Methodological Quality

AMSTAR-2 (Shea et al., 2017) was used to evaluate the methodological quality of the included SRs/MAs. This tool consists of 16 items and includes seven key items (2, 4, 7, 9, 11, 13, and 15). According to the judgment criteria of AMSTAR-2, each item was evaluated as “Yes”, “Partial Yes”, or “No”. SRs/MAs with no or only one non-critical item weakness were rated as high quality; more than one non-critical item weakness was rated as moderate quality; one critical flaw with or without non-critical item weakness was rated as low quality; and more than one critical flaw with or without non-critical item weaknesses was rated as extremely low quality. Two researchers (GF and XF) independently evaluated the methodological quality. Any disagreements were resolved with the help of a third researcher (WS).

2.5 Reporting Quality

The PRISMA statement was used to evaluate the reporting quality of the included SRs/MAs and included a 27-item checklist. Each item was evaluated as “Yes,” “Partial Yes,” or “No” based on seven domains: title, abstract, introduction, methods, results, discussion, and funding (Liberati et al., 2009; Moher et al., 2009). Two researchers (GF and XF) independently evaluated the reporting quality. Any disagreements were settled through dialogue with a third researcher (WS).

2.6 Quality of Evidence

The GRADE system was used to evaluate the quality of evidence, classifying a study into one of four levels: high, moderate, low, or very low. The evidence quality of included SRs/MAs was rated based on five factors: risk of bias, inconsistency, imprecision, indirectness, and publication bias. Two researchers (GF and XF) independently assessed the evidence quality. Any disagreements were resolved through discussion with a third researcher (WS).

2.7 Data Synthesis

A descriptive analysis of the included SRs/MAs was used in this overview. Risk ratios (RR), odds ratios (OR), 95% confidence intervals (CI), weighted mean differences (WMD), and standard mean differences (SMD) were included to summarize the outcomes. I² was used to detect the heterogeneity of each included SR/MA.

3 Results

3.1 Literature Selection

A total of 3368 items were discovered from the eight databases. NoteExpress 3.2.0 document manager was used for the literature selection. After the preliminary screening and elimination of duplicates, 157 articles were obtained for full-text reading. This overview ultimately included a total of 16 articles (Zhao et al., 2008; Chen et al., 2015; Xiao et al., 2015; Lai, 2017; Liu, 2018; Shan et al., 2018; Sun et al., 2018; Tian et al., 2018; Wang et al., 2019; Chen, 2020; Lei et al., 2020; Li et al., 2020; Lyu et al., 2020; Wu et al., 2020; Yu, 2020; Zhai et al., 2022). Figure 1 shows the entire study selection procedure.

FIGURE 1

FIGURE 1. Flow diagram of the study process.

3.2 Study Characteristics

Of the 16 SRs/MAs, 14 studies were published as journal articles, and two (Lai, 2017; Yu, 2020) were published as dissertations. These SRs/MAs were published between 2008 and 2022. Eleven SRs/MAs were published in Chinese and five (Xiao et al., 2015; Shan et al., 2018; Wang et al., 2019; Lyu et al., 2020; Wu et al., 2020) in English. The SRs/MAs all included migraine patients. Most SRs/MAs did not define the type of treatment, except one that described the type of intervention, which was preventive treatment (Lyu et al., 2020). Seven outcome measures were collected in 16 SRs/MAs, including migraine days, acute medication usage, responder rate, pain intensity, migraine frequency, migraine duration, and adverse events. The study characteristics are shown in Table 2.

TABLE 2

TABLE 2. Systematic review/meta-analysis characteristics.

3.3 Description of Chinese Herbal Medicine

A total of 74 CHM formulas were found in these studies, including 64 decoctions and 10 patent medicines. All herbs appeared 671 times. The top seven most frequently used herbs were Rhizoma Ligustici Chuanxiong (64/9.54%), Radix Angelicae Dahuricae (38/5.66%), Radix Paeoniae Alba (27/4.02%), Radix Glycyrrhizae Uralensis (26/3.87%), Radix Angelicae Sinensis (25/3.73%), Rhizoma Gastrodiae (21/3.13%), and Herba Asari (21/3.13%). Table 3 shows the details of these seven herbs. The top three most frequently used CHM patent medicines were Yangxue Qingnao granules, Zhengtian pills, and Toutongning capsules. Details are provided in Table 4.

TABLE 3

TABLE 3. Details of frequently used herbs in CHM formulas.

TABLE 4

TABLE 4. Composition of Chinese patent medicines used in the included studies.

3.4 Methodological Quality

We evaluated the methodological quality of 16 SRs/MAs. As shown in Table 5, the methodological quality of all the included SRs/MAs was extremely low. For the evaluation of key items, the protocol was rarely registered before the commencement of the review and was only registered in one SR/MA (Lyu et al., 2020). None of the SRs/MAs offered a list of excluded studies or explained their exclusion. Eight SRs/MAs were appraised as “No” for key item 11 because the necessary statistical approaches for substantial heterogeneity were not applied. When analyzing and discussing the outcomes of their reviews, six SRs/MAs (Liu, 2018; Sun et al., 2018; Tian et al., 2018; Chen, 2020; Li et al., 2020; Zhai et al., 2022) did not emphasize assessing the risk of bias.

TABLE 5

TABLE 5. Results of the AMSTAR 2 assessment.

3.5 Reporting Quality

As shown in Table 6, 20 of 27 items were well-reported, with a response rate of “Yes” or “Partial Yes” exceeding 80%. However, 7 of these 27 items were inadequately reported, especially for item 5 (Protocol and registration), item 8 (Search), and item 27 (Funding), with a less than 50% response rate of “Yes” and “Partial Yes.” Only one SR/MA (Lyu et al., 2020) was registered before the review began. Two SRs/MAs (Lei et al., 2020; Yu, 2020) presented an electronic search approach for at least one database. Two SRs/MAs (Wang et al., 2019; Lyu et al., 2020) described the sources of funding for the SR/MAs and described the role of funders in the systematic review.

TABLE 6

TABLE 6. Results of the PRISMA assessment.

3.6 Effects of Chinese Herbal Medicine Interventions

3.6.1 Migraine Days

3.6.1.1 Chinese Herbal Medicine vs. Placebo-Controlled

Two SRs/MAs (Chen et al., 2015; Shan et al., 2018) reported migraine days, and the results demonstrated that CHM was superior to PC in improving migraine days.

3.6.1.2 Chinese Herbal Medicines vs. Western Medicines

Migraine days were assessed in three SRs/MAs (Lai, 2017; Shan et al., 2018; Lyu et al., 2020), but did not arrive at consistent conclusions: two showed that CHM was similar to WM, while one showed CHM was better than WM in reducing migraine days.

3.6.2 Responder Rate

Responder rate was assessed in two SRs/MAs (Xiao et al., 2015; Lyu et al., 2020): one SR (Lyu et al., 2020) indicated that CHM improved responder rate compared with WM; another SR (Xiao et al., 2015) also showed that CHM was better than PC.

3.6.3 Pain Intensity

3.6.3.1 Chinese Herbal Medicine vs. Placebo-Controlled

Pain intensity was evaluated in four SRs/MAs (Chen et al., 2015; Xiao et al., 2015; Shan et al., 2018; Yu, 2020). Three SRs/MAs (Chen et al., 2015; Xiao et al., 2015; Shan et al., 2018) concluded that CHM was better than PC in terms of pain intensity.

3.6.3.2 Chinese Herbal Medicines vs. Western Medicines

Six SRs/MAs (Lai, 2017; Liu, 2018; Lyu et al., 2020; Wu et al., 2020; Yu, 2020; Zhai et al., 2022) reported pain intensity, and three of them evaluated VAS. Of these three, two SRs/MAs (Liu, 2018; Wu et al., 2020) indicated that CHM was inferior to WM in reducing headache intensity. One SR (Lyu et al., 2020) was performed for a subgroup analysis based on treatment duration. In the SR by Lyu et al. (2020), CHM was found to be better than WM in reducing headache intensity at the end of treatment, while there was no significant difference at the end of follow-up. One SR (Yu, 2020) evaluated pain intensity by NRS, which showed CHM was similar to WM at improving pain intensity. Three SRs/MAs (Lai, 2017; Shan et al., 2018; Zhai et al., 2022) reported pain intensity: two (Lai, 2017; Shan et al., 2018) showed that CHM noticeably reduced pain intensity compared with WM, while no statistical difference was found in the study by Zhai et al. (2022).

3.6.3.3 Chinese Herbal Medicine Plus Western Medicines vs. Western Medicines

Eight SRs/MAs (Sun et al., 2018; Tian et al., 2018; Wang et al., 2019; Chen, 2020; Lei et al., 2020; Li et al., 2020; Yu, 2020; Zhai et al., 2022) evaluated pain intensity of CHM plus WM; seven of these articles measured VAS, and two SR (Lai, 2017; Zhai et al., 2022) combined VAS and NRS scores. All showed that CHM plus WM had a better effect in reducing pain intensity than WM alone.

3.6.4 Migraine Frequency

3.6.4.1 Chinese Herbal Medicine vs. Placebo-Controlled

Migraine frequency was evaluated in four SRs/MAs (Chen et al., 2015; Xiao et al., 2015; Shan et al., 2018; Yu, 2020). Three of these (Chen et al., 2015; Xiao et al., 2015; Shan et al., 2018) showed that CHM was superior to PC in reducing migraine frequency. One SR (Yu, 2020), including 438 participants in two RCTs, indicated that CHM and WM were equally effective.

3.6.4.2 Chinese Herbal Medicines vs. Western Medicines

Eight SRs/MAs (Zhao et al., 2008; Lai, 2017; Liu, 2018; Shan et al., 2018; Lyu et al., 2020; Wu et al., 2020; Yu, 2020; Zhai et al., 2022) assessed migraine frequency, while only one SR (Lai, 2017) described units of migraine frequency, including the number of attacks per month and headache attack score. Except for in one SR (Yu, 2020), these SRs/MAs showed that CHM was more effective than WM alone in improving migraine frequency.

3.6.4.3 Chinese Herbal Medicine Plus Western Medicines vs. Western Medicines

Three SRs/MAs (Tian et al., 2018; Lei et al., 2020; Zhai et al., 2022) investigated the effectiveness of CHM plus WM on migraine frequency. A meta-analysis of these SRs/MAs found that CHM plus WM significantly improved migraine frequency compared with WM alone.

3.6.5 Migraine Duration

3.6.5.1 Chinese Herbal Medicine vs. Placebo-Controlled

Two SRs/MAs (Chen et al., 2015; Shan et al., 2018) indicated CHM significantly improved migraine duration compared with PC.

3.6.5.2 Chinese Herbal Medicines vs. Western Medicines

Migraine duration was assessed in six SRs/MAs (Zhao et al., 2008; Lai, 2017; Shan et al., 2018; Lyu et al., 2020; Yu, 2020; Zhai et al., 2022). Three SRs/MAs showed that CHM was superior to WM in reducing migraine duration (Lai, 2017; Shan et al., 2018; Zhai et al., 2022), whereas the results of the meta-analysis were inconsistent in the studies by Yu (2020) and Zhao et al. (2008). One SR/MA (Lyu et al., 2020) was performed for subgroup analysis based on treatment duration. In Lyu et al. (2020), CHM was found to be better than WM in improving migraine duration at the end of treatment, while there was no significant difference at the end of follow-up.

3.6.5.3 Chinese Herbal Medicines Plus Western Medicines vs. Western Medicines

Three SRs/MAs (Chen et al., 2015; Lei et al., 2020; Zhai et al., 2022) assessed migraine duration and showed that CHM plus WM could improve migraine duration compared with WM alone.

3.6.6 Acute Medication Usage

Only one SR (Lyu et al., 2020) reported the use of acute medication. The meta-analysis showed that CHM was better than WM in terms of acute medication usage.

3.6.7 Adverse Events

Adverse events were evaluated in eight SRs/MAs, with the main adverse events being digestive symptoms, including nausea, diarrhea, and ventosity. In general, these SRs/MAs showed that there was no difference between CHM and WM with regard to adverse events, except for two SRs/MAs which stated that the incidence of adverse events with CHM was lower than with WM.

3.6.8 Summary of Quality of Evidence

A total of 69 outcomes were assessed using the GRADE system. The results showed that the quality of evidence was moderate in 1 study, low in 13, and very low in 55. No outcomes were assessed as high quality. The downgrading factors were risk of bias (n = 69), inconsistency (n = 40), imprecision (n = 39), and publication bias (n = 61). The details of the quality of evidence are shown in Table 7

TABLE 7

TABLE 7. GRADE profile for the quality of evidence.

4 Discussion

4.1 Main Findings

This study covered 16 SRs/MAs published between 2008 and 2022. Eleven SRs/MAs were published in Chinese and five (Xiao et al., 2015; Shan et al., 2018; Wang et al., 2019; Lyu et al., 2020; Wu et al., 2020) in English. The SRs/MAs that were published in English were more standardized in terms of methodological and reporting quality than the majority of those published in Chinese, particularly regarding the reporting of possible conflicts of interest. We established three main findings by evaluating the methodological and evidence quality of the SRs/MAs published to date.

First, for this overview we used a narrative description of the data synthesis used in these SRs/MAs, which showed that CHM plus WM had a favorable effect on migraines. In comparison, there was conflicting evidence for the effectiveness of using CHM alone. Twelve SRs/MAs investigated the efficacy of CHM alone as a migraine treatment and found that CHM was better than WM in improving responder rate and acute medication usage, and was superior to placebo in improving migraine days, responder rate, and migraine duration. However, there was insufficient evidence to verify the effectiveness of CHM in migraine treatment with regard to pain severity and migraine frequency. Our findings indicate that CHM appears to be safe for migraine treatment. According to the data synthesis of the included SR/MA outcomes, we found that total efficiency was the most extensively used outcome indicator in the SRs/MAs and the original RCTs. However, this outcome indicator was a composite index; the efficacy evaluation criteria were usually self-designed or referred to in other literature. Therefore, it is challenging for this indicator to accurately reflect the efficacy of a treatment (Zhang et al., 2020). Therefore, we did not evaluate total efficiency due to these factors.

Second, the methodological quality and reporting of the included SRs/MAs was extremely low. High-quality SRs/MAs could provide sufficient evidence for clinical decision-making. It was common for us to overlook the program registration in the 16 SRs/MAs, which could reduce a study’s rigor. None of the SRs/MAs provided a list of excluded studies or explained their exclusion, which might lead to selection bias. Also, commercially funded studies are more likely to achieve results that favor the funder’s product. However, none of these systematic evaluations, including the RCTs, reported funding sources, which might lead to publication bias.

Third, 69 outcomes were assessed using the GRADE system; this showed that the quality of pooled evidence in these SRs/MAs was deficient. Therefore, we should be cautious about drawing conclusions based on their results. The main downgrading factor was risk of bias. All of the SRs/MAs included original RCTs that were of low-quality, lacking detailed descriptions of randomization, allocation concealment, and blinding techniques. SRs/MAs of studies with small sample sizes are more likely to have publication bias (Guyatt et al., 2011), as most of the included SRs/MAs in our study did. High heterogeneity was also a major cause of lower levels of evidence quality in 13 SRs/MAs. Just four SRs/MAs explained and dealt with high heterogeneity; three of them (Lai, 2017; Lei et al., 2020; Yu, 2020) used subgroup analysis, and three of them (Lei et al., 2020; Yu, 2020; Zhai et al., 2022) used sensitivity analysis. By extracting the included SR outcomes, we found that the evaluation criteria for the outcomes of CHM for migraine were not uniform, especially for total efficiency rate and migraine frequency.

4.2 Comparison with Current Recommendations

A clinical practice guideline for treating migraines using CHM has recently been published in China, which recommends five classic formulas (Chuanxiong Chatiao powder, Chuanxiong Dingtong Yin, Sanpian Decoction, Xuefu Zhuyu decoction, and Tongqiao Huoxue decoction) and four Chinese patent medicines (Zhengtian pills, Toutongning capsules, Tongtian oral liquid, and Yangxue Qingnao granules/pills); these treatments, alone or in combination with WM, have an effect on migraine, but the quality of evidence is generally low (Xu et al., 2020). The findings of our study were consistent with these recommendations. Due to the generally low quality of evidence, recent international guidelines have not yet recommended herbal medicine for migraines (American Headache Society, 2018; Araki et al., 2019; Steiner et al., 2019). An overview evaluating the evidence from SRs/MAs of CAM therapy for the prevention and treatment of migraine headaches was recently published (Posadzki et al., 2015). The authors evaluated SRs/MAs of herbal medicines, including Ginkgo biloba, Petasites hybridus, and Tanacetum parthenium L, which differed from our inclusion criteria. Our study aimed to evaluate the evidence relating to Chinese herbal formulas. We conclude that the evidence for the effectiveness of herbal medicine is conflicting.

4.3 Limitations

Our investigation had several limitations. First, due to the small number of systematic evaluations of individual drugs for migraine, we did not evaluate individual drugs. Second, individual herbal medicine treatments varied throughout the included SRs/MAs, as did the efficacy criteria. As a result, we did not quantitatively pool the evidence of all outcomes and simply described the evidence of the included studies.

4.4 Implications for Future Studies

Our results provide valuable evidence of the definitive effectiveness of CHM in the treatment of migraines. We have developed the following recommendations for future studies. First, systematic evaluations should be established in accordance with the PRISMA guidelines (Page et al., 2021), to improve their methodological quality and render their evidence more convincing. Second, clinical studies should employ enhanced methodological quality, such as the proper application of randomization, allocation concealment, and blinding methods. Third, the design of the clinical study protocol is equally essential. Investigators should consult the most recent controlled trial guidelines for preventive treatment of chronic migraine in adults (Tassorelli et al., 2018). To select outcome indicators in systematic assessments or clinical research, the efficacy evaluation criteria of outcome indicators should be clarified, and composite indicators should be used sparingly (Zhang et al., 2020).

This overview suggests that CHM may be beneficial in improving migraines and can be used as a complementary therapy. However, due to the low quality of both methodology and evidence, we should treat the conclusions of included studies cautiously. Thus, future studies should focus on improving the methodological and reporting quality of SRs/MAs to make our conclusions more clinically applicable, and standardized clinical study designs should be employed to provide clinicians with reliable evidence.

Author Contributions

GF, WS, and YZ designed the study. GF, XF, WS, and YZ contributed to the literature search, data selection, extraction, and quality assessment. GF, MJ, and SL generated the figure and tables. XL and JW performed the data analyses. GF, WS, and YZ wrote and proofread the manuscript.

Funding

This research was supported by the Scientific and Technological Innovation Project of the China Academy of Chinese Medical Sciences (No. CI2021B006), Capital’s Funds for Health Improvement and Research (No. 2020-2-4173), the National TCM Leading Personnel Support Program (NATCM Personnel and Education Department (2018) (No. 12), the Innovation Team and Talents Cultivation Program of National Administration of Traditional Chinese Medicine (No. ZYYCXTD-C-202007), and the China Academy of Chinese Medical Sciences Innovation Fund (No. CI2021A01301, CI2021A00911).

Conflict of Interest

The authors declare that this research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s Note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Abbreviations

CAM, complementary and alternative medicine; CGRP, calcitonin gene-related peptide; CHM, Chinese herbal medicine; CI, confidence interval; GRADE, Grading of Recommendations Assessment, Development and Evaluation; MA, meta-analysis; NRS, numerical rating scale; OR, odds ratio; PC, placebo-controlled; PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-analyses; RR, risk ratio; SMD, standard mean difference; SR, systematic review; VAS, visual analog scale; WM, Western medicine; WMD, weighted mean difference.

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