Table 8 and Figure 8A show the top 10 keywords with high frequency and centrality. The frequency of “acupuncture,” “migraine,” and “pain” ranked the top three, and the centrality of “acupuncture therapy,” “tension type headache,” and “acupuncture analgesia” ranked the top three. We use a time zone graph to demonstrate the evolution of keywords over time (Figure 8B). Keywords are positioned on the vertical axis, and time is on the horizontal axis, with the direction pointing to the right. From 2003 to 2023, the changes in high-frequency keywords over time are clearly presented. This study categorizes the prominent keywords in the past 21 years based on headache type, acupuncture stimulation type, safety, mechanism of action, disease impact, and research methods, etc., as indicated in Table 9:

(1) Headache types: The top five ranked headache types are “migraine,” “tension type headache,” “chronic headache,” “cervicogenic headache,” and “cluster headache.” This indicates that primary headaches are the most extensively studied, with migraine being the most researched subtype, aligning with basic epidemiological patterns.

(2) Acupuncture stimulation types: The top five ranked acupuncture stimulation types are “filiform needle acupuncture,” “electroacupuncture,” “sham acupuncture,” “auricular acupuncture,” and “acupoint pressure.” This suggests that research on acupuncture treatment for headaches is most prevalent. Experimental processes often involve blank controls, waiting lists, standardized sham acupuncture, ritualized sham acupuncture, sham acupuncture, sham electroacupuncture, and Western medication. Studies utilizing moxibustion as a stimulation method have yet to be reported.

(3) Safety: Most studies do not report adverse events from acupuncture. However, some research indicates an adverse event rate of approximately 8.6% associated with acupuncture. Common adverse reactions include minor bleeding or hematoma (6.1%), pain (1.7%), and vegetative symptoms (0.7%) (Witt et al., 2009). Adverse reactions resulting from negligence or medical accidents (such as forgotten or broken needles, pneumothorax, and burns after moxibustion) account for around 0.1%. Furthermore, the interpretation of adverse events is subjective. For instance, sensations of soreness, numbness, heaviness, or distention after acupuncture, which clinicians view as indications of therapeutic efficacy, might be considered adverse reactions by patients. Therefore, when administered by adequately trained and experienced practitioners, acupuncture proves to be a highly safe practice, with rare instances of severe adverse events.

(4) Mechanisms of action: The top five mechanisms of acupuncture’s analgesic effects include “neuromodulation,” “opioid peptides,” “5-HT receptors,” “neurohormone,” and “functional connectivity,” highlighting the central role of neural modulation in acupuncture’s pain relief. Acupuncture can modulate neuronal activity, activating or inhibiting the central and peripheral nervous systems, thereby effectively reducing pain perception (Chen et al., 2023). Notably, “opioid peptides” and “5-HT receptors” play critical roles in this process (Lin et al., 2022). Research reveals that the endogenous opioid peptides in the central nervous system are crucial for the analgesic effect of electroacupuncture (EA), with different frequencies of EA releasing different types of neuropeptides. For instance, 2 Hz EA promotes the release of endorphins, enkephalins, and dynorphins, while 100 Hz EA specifically enhances the release of dynorphins (Han, 2004). Additionally, acupuncture-induced release of 5-HT at acupoints contributes to its analgesic effect, with ATP secretion mediated by 5-HT1A receptors possibly being a potential mechanism (Li et al., 2023). Acupuncture can also regulate the neuroendocrine system, inducing analgesia by affecting the secretion and balance of hormones. Studies show that EA increases the content of norepinephrine and the expression of β2-adrenergic receptors in inflamed tissues, thus alleviating pain (Shi et al., 2023). The latest research gradually reveals the deep mechanisms of acupuncture in relieving pain, especially its close connection with brain functional connectivity (Otti and Noll-Hussong, 2012). Acupuncture can change brainwave activity patterns and regulate the activity of brain regions related to pain perception and processing, thus affecting pain perception and cognition (Zhang et al., 2020b). In summary, the analgesic mechanism of acupuncture is a complex network regulation process covering multiple biological pathways and mechanisms. These mechanisms may vary depending on the type of pain, chosen acupoints, and individual differences.

(5) Popular attention: Public focus on the disease predominantly centers around terms like “efficacy,” “pain,” “prophylaxis,” “prevalence,” and “quality of life.” These focal points reflect society’s expectations and demands for acupuncture as a treatment method to alleviate and prevent headaches.

(6) Research methods: Keywords such as “randomized controlled trial,” “double-blind,” “clinical trial,” “multicenter,” and “placebo” indicate that most studies on acupuncture for treating headaches employ randomized controlled trials. From the perspective of evidence-based medicine, evidence derived from randomized controlled trials is regarded as the highest level of the evidence pyramid, offering strong support for the clinical utilization of acupuncture in the treatment of headaches (Bhide et al., 2018).

(7) Efficacy: High-quality meta-analysis and systematic reviews indicate that acupuncture is effective for migraine, tension-type headache, chronic pain, and cervicogenic headache, making it a favorable option for headache patients (Sun and Gan, 2008; France et al., 2014; Millstine et al., 2017; Lu et al., 2022; Tao et al., 2023).

The keywords clusters are shown in Figure 8C. The network contained 208 nodes and 311 links. The largest CC was 98%, indicating a high concentration of major research areas or topics; the Modularity Q was 0.7515 (>0.5), suggesting that the network clusters were well-defined and reasonable, and the Mean Silhouette S was 0.9026 (>0.5), indicating that the clusters demonstrated acceptable homogeneity (Chen, 2006). In this network, more important clustering labels were listed in 10 clusters, including “#0 migraine(21),” “#1 chronic headache(21),” “#2 migraine without aura(20),” “#3 cluster headache (20),” “#4 multicenter(17),” “#5 tension type headache(16),” “#6 opioids(16),” “#7 myofascial pain(15),” “#8 complementary therapies(15),” “#9 efficacy(15),” as depicted with varying colors.

Utilizing the burst detection algorithm in CiteSpace software, this paper conducts keyword burst detection and analysis for 808 articles from the WoS core database. Synonymous keyword nodes are merged, with a minimum duration of 2 years, state transition value at 1, and state difference ratio at 2. This process identifies the top 25 keywords with the highest burst intensities. The distribution of burst times and durations for the top 25 burst keywords is illustrated in Figure 8D. Light blue stripes indicate that the keyword has not yet appeared, dark blue stripes indicate that the keyword has appeared, and red stripes indicate the time period when the keyword has exploded.

Based on the burst detection results, the keyword with the greatest emergences was “placebo” (8.96). Keywords with burst durations exceeding 5 years include “placebo” (2003–2010), “physiotherapy” (2005–2012), “trial” (2005–2011), “chronic headache” (2005–2013), “primary care” (2006–2012), and “functional connectivity” (2018–2023). This indicates the pivotal roles these aspects have played in acupuncture headache research.

From a time perspective, studies from 2003 to 2018 mainly used clinical trials, and multi-center and large-sample randomized controlled clinical trials showed higher research quality and credibility. The emergence of keywords in 2018–2020 reflects the continual rise of systematic reviews during this period. Systematic reviews aim to synthesize and integrate existing study results to derive the best evidence synthesis, making them a pivotal source of evidence-based medical research. During 2020–2023, the keywords “functional connectivity,” “guideline,” “safety,” “disease,” “depression,” and “therapy” had the highest number of outbreaks.

Headache, as a non-specific symptom, can be associated with various diseases or pathological states. Based on keyword analysis, the research hotspots in this field primarily centers around the efficacy of acupuncture in preventing and treating migraines. In the past decades, acupuncture has been pointed out as a valuable non-pharmacological tool in patients with migraine. In acupuncture research, true acupuncture is often compared with sham acupuncture. There are many different types of sham acupuncture intervention; these include lack of skin penetration by the needle, shallow penetration of the needle, insertion at points that are not traditional acupuncture points, or not achieving “deqi” which is an expected needling response (subjective sensation of local warmth, paresthesia tenderness) that is considered an integral element of the healing process (Zhang et al., 2020a). The efficacy of acupuncture was also reported in comparison with pharmacological treatment in episodic migraine (Hesse et al., 1994; Allais et al., 2002; Diener et al., 2006; Streng et al., 2006; Wang et al., 2011; Facco et al., 2013; Zhang et al., 2020a). The majority of these studies compared acupuncture with monotherapy as a prophylactic treatment. However, recently, one prospective, randomized controlled, study compared acupuncture with the best prophylactic drugs for patients taking into consideration comorbidities (i.e., depression, insomnia, hypertension, etc.) and previous preventive treatment (Giannini et al., 2021). This trial showed that acupuncture was as effective as the more appropriate pharmacological treatment for migraine prophylaxis. Together, this data, support the efficacy of acupuncture in migraine prophylaxis. Furthermore, the neural mechanisms of acupuncture for migraine treatment have garnered increasing attention. Neuroimaging studies suggest that acupuncture may alter aberrant functional activity and connectivity in the descending pain modulation system, default mode network, thalamus, anterior cingulate cortex, posterior cingulate cortex, and cerebellum. Acupuncture regulates peripheral and central sensitization, normalizes abnormal brain activity, and thus inhibits the transmission of pain signals (Chen et al., 2022). Additionally, tension-type headache has been a focus. The Cochrane systematic review database acknowledges acupuncture’s effectiveness in treating frequent episodic or chronic tension-type headaches, indicating its potential value as a treatment approach (Linde et al., 2016). Furthermore, studies have explored cervical headaches, cluster headaches, neuralgia headaches, occipital neuralgia, secondary headaches due to stroke, secondary headaches due to hypertension, and other diseases. While there have been published papers, further exploration of these conditions and systematic research is still required.

Acupuncture and moxibustion therapy have a variety of stimulation methods, providing a variety of options for headache treatment, of which acupuncture is the majority. Filiform needle acupuncture and electroacupuncture are the most common needling methods for headache treatment. Filiform needle acupuncture is widely applied, benefiting from extensive scientific research support, accumulated clinical evidence, personalized treatment advantages, and a relatively low risk of side effects. It plays a crucial and significant role in clinical practice. Next is electroacupuncture based on filiform needle acupuncture. Compared to filiform needle acupuncture alone, electroacupuncture offers advantages such as repeatable operations, controllable stimulation intensity, and excellent analgesic effects. It is increasingly recognized and applied by researchers and medical professionals. Furthermore, literature reports also address therapies like moxibustion, warm needle acupuncture, scalp acupuncture, eye acupuncture, ear acupuncture, laser acupuncture, acupoint injection, small needle knife therapy, and acupuncture combined with tuina massage for headache treatment. However, these studies lack substantial sample sizes and high-quality research evidence to establish their therapeutic advantages. Therefore, future research employing large samples, multicenter, and high-quality clinical research designs will help clarify the therapeutic advantages of these methods, identify their most suitable symptomatic characteristics, and further promote the development and application of acupuncture therapy in headache treatment.

The safety and effectiveness of acupuncture for headaches have always been a focus. Acupuncture treatment for headaches is associated with high participant satisfaction and a low likelihood of adverse events, making it considered a very safe and effective intervention (MacPherson, 2004). For patients unwilling or unable to use medication for prevention, particularly children or adolescents, acupuncture for headache treatment can be recommended (Doll et al., 2019). Moreover, a research suggested acupuncture as a potential non-pharmacological approach for managing acute pain in pediatric emergency departments (Tsai et al., 2018). Another research found that acupuncture is an effective strategy for treating acute pain and may help prevent or reduce opioid dependency (Nielsen et al., 2022a). The effectiveness of acupuncture in the management of acute pain has been validated, establishing it as a crucial component of comprehensive acute pain care. Therefore, it is necessary for future research to conduct pragmatic, multicenter, well-defined acupuncture randomized controlled trials in emergency departments to clarify the dosage and universality of acupuncture treatment for acute pain (Nielsen et al., 2022b).

With the continuous expansion of the research field of acupuncture analgesia, researchers have moved beyond merely focusing on exploring the role of acupuncture in regulating pain sensation. Currently, the interaction between acupuncture, pain, and emotional disorders has become a hot topic of research. Numerous studies have revealed that chronic pain and psychological health disorders share common neurobiological mechanisms (Nalini Vadivelu et al., 2017); the application of functional imaging technology further demonstrates that brain regions associated with pain-related emotions and perceptions overlap with those affected in patients with depression (Ehnvall et al., 2009). In terms of treatment, psychological interventions and antidepressants are generally beneficial for pain management (Hooten, 2016). These evidences support a close interrelationship between chronic pain and emotional disorders. Acupuncture can exert a bidirectional and holistic regulatory effect on both aspects. Not only can it alleviate pain, but it can also regulate emotional states. A retrospective cohort study found that acupuncture can not only reduce the severity of headaches in migraine patients but also lower the risk of depression and anxiety (Liao et al., 2020). For chronic pain, acupuncture has been shown to improve pain and psychological disorders (Lin et al., 2020). Additionally, the role of acupuncture in regulating emotions to facilitate pain relief cannot be overlooked. Studies indicate that a good mental state can reduce the number of days migraine patients suffer from headaches, suggesting that the patient’s emotional state is one of the most important non-specific factors in improving the analgesic effect of acupuncture (Pokladnikova et al., 2019). Further research reveals that acupuncture can regulate the brain’s reward/motivation circuits to modulate pain responses (Lee et al., 2015). A study shows that acupuncture can modulate the activity of the brain’s limbic lobes and subcortical structures. The limbic system is a set of key structures in the brain responsible for processing emotions and memory, including areas such as the prefrontal cortex, anterior cingulate cortex, amygdala, hippocampus, and hypothalamus (Hui et al., 2000). When acupuncture achieves “deqi,” these areas exhibit negative activation, and this phenomenon is closely related to the brain’s endogenous pain regulation system (Hui et al., 2005). Another study further elucidated that acupuncture can alleviate pain aversion by promoting the release of opioid substances and 5-HT in the brain’s reward/motivation circuit and by upregulating the expression of GluA1, mGluR1, and GABAB2 proteins in the amygdala, thereby exerting an analgesic effect at the holistic level (Hu, 2019). This is akin to the concepts in traditional Chinese medicine of “alleviating pain and tranquilize” and “regulating the spirit to relieve pain.” Therefore, the mechanisms by which acupuncture treats headaches and emotional disorders warrant further in-depth exploration in the future.

The modern mechanism of acupuncture treatment of headache has been more studied in recent years. Scholars have observed the connection between headaches and the brain, and with the aid of neuroimaging techniques, investigating brain functional connectivity has emerged as a new research focus. Functional connectivity refers to the synchronized neural activity between different brain regions under specific tasks or states, which can be detected and studied using various neuroimaging techniques such as functional magnetic resonance imaging (fMRI) and electroencephalograph (Zhao et al., 2023). More and more studies suggest that functional connectivity networks are closely linked to acupuncture mechanisms, with central integration playing a pivotal role in acupuncture mechanisms (Cai et al., 2018). Supported by fMRI technology, studies discovered that abnormal functional connectivity of the thalamus may be a mechanism underlying the onset and development of migraines (Tian et al., 2021). Another study demonstrated that migraines’ typical pathological feature is abnormal pain processing, with significant functional connectivity abnormalities in the frontal, parietal, and limbic regions (Cao et al., 2022). Therefore, acupuncture can alleviate headache symptoms by restoring pain processing function and regulating pain sensation. Current research proposed that acupuncture might simultaneously regulate the resting state-functional connectivity of two pain-modulating regions—the amygdala and the middle cingulate cortex (Liu et al., 2022). The middle and superior temporal gyrus could be key nodes associated with multisensory processing relevant to acupuncture treatment for migraine regulation. Compared to the period before 2020, the field predominantly relied on clinical trials to demonstrate the effectiveness of acupuncture for treating headaches without clearly understanding its underlying mechanisms. Through the use of neuroimaging techniques, it is now possible to precisely identify the specific brain area affected by acupuncture treatment for headaches. Such research exploring the relationship between acupuncture and functional connectivity is of significant importance for gaining deeper insights into disease mechanisms and developing more effective treatment methods, which in turn aid in early diagnosis, treatment, and disease assessment.

Moreover, imaging technology features assist in predicting the effects of acupuncture. Yang XJ suggested that pre-treatment brain structure could be a new predictive indicator for acupuncture treatment outcomes in migraine without aura (Yang et al., 2020). One study proposed that baseline low-frequency fluctuations in brain regions associated with cognitive pain regulation could predict future improvements in headache intensity in acupuncture-treated patients (Zhengjie et al., 2020). Another finding presented the potential and effectiveness of utilizing machine learning techniques and individual patterns of spontaneous brain activity to forecast the outcomes of acupuncture treatment for migraine without aura (Yin et al., 2020). Hence, with the continuous development of neuroimaging technology, the prospects for studying the relationship between headaches and brain functional connectivity will become even more promising.