Qi, the invisible life-force said to flow through channels called meridians, is the foundational concept behind acupuncture, but no laboratory has ever isolated a substance or energy that matches the traditional description. What researchers have found instead is a set of real, measurable physiological events triggered by needle insertion: connective tissue deformation, endorphin and adenosine release, shifts in brain activity, and changes in blood flow and immune signaling. These discoveries do not prove or disprove qi as a philosophical concept, but they have begun to give acupuncture a biological vocabulary that sits alongside (and sometimes in tension with) the classical one.
What Qi and Meridians Actually Mean in Traditional Theory
In traditional Chinese medicine, qi is not a single substance. It is a broad organizing concept for the body’s functional activity: digestion, circulation, immune defense, warmth, and movement all fall under different categories of qi. Health depends on qi circulating smoothly through a network of meridians, and disease arises when that circulation is blocked or deficient. Acupuncture aims to restore flow by stimulating specific points along these channels. Meridian theory remains one of the core frameworks in traditional Chinese medicine, providing the logic for how acupuncture points are selected, which conditions are treated, and why a needle in the lower leg might affect a headache or a digestive complaint.1PubMed Central. Classic and Modern Meridian Studies: A Review of Low Hydraulic Resistance Channels along Meridians and Their Relevance for Therapeutic Effects in Traditional Chinese Medicine Meridians also serve as the theoretical basis for herbal medicine, moxibustion (heat therapy), and acupressure massage.2Acupuncture and Herbal Medicine. Scientific exploration and hypotheses concerning the meridian system in traditional Chinese medicine
The challenge for modern science is that qi, as traditionally described, does not map neatly onto any single anatomical or physiological entity. It is not blood, not nerve impulses, not lymph, though various researchers have proposed partial overlaps with each. This has led to a productive but sometimes frustrating research direction: rather than trying to “find” qi, investigators have focused on what is physically happening at acupuncture points and along meridian pathways.
What Lies Beneath the Acupuncture Points
One of the most consistent findings has been the relationship between acupuncture points and connective tissue. A landmark anatomical study examined postmortem tissue sections and found roughly 80% correspondence between recognized acupuncture point locations and intermuscular or intramuscular connective tissue planes.3PubMed. Relationship of acupuncture points and meridians to connective tissue planes These are the thin sheets of tissue that separate and connect muscles, and they are rich in nerve endings, blood vessels, and immune cells.
Imaging studies using CT and MRI have pushed this idea further, proposing that the body’s fascial network, the web of connective tissue that envelops muscles, organs, and bones, may be the anatomical basis of the meridian system.4PubMed. Possible applications for fascial anatomy and fasciaology in traditional Chinese medicine Fascia was long dismissed as mere packing material, but it is now recognized as a mechanically active tissue with its own sensory nerve supply. Whether or not fascia “is” the meridian system, it provides a plausible physical substrate for the idea that stimulating a needle at one point can send a signal along a tissue plane to affect distant body regions.
What the Needle Actually Does to Tissue
When a practitioner inserts and rotates an acupuncture needle, the tissue physically winds around the shaft like spaghetti around a fork. This creates a phenomenon called “needle grasp,” where the tissue grips the needle and the force needed to pull it out increases. Research has shown that connective tissue winding, rather than muscle contraction, is responsible for this effect. Rotation increases both the pull-out force and the volume of subcutaneous tissue engaged, and produces more organized collagen architecture around the needle.5PubMed. Evidence of connective tissue involvement in acupuncture Laboratory models using collagen gels confirm that simulated needle rotation produces circumferential alignment of collagen fibers near the needle, shifting to radial alignment further away.6PubMed Central. An in vitro assay of collagen fiber alignment by acupuncture needle rotation
This mechanical deformation matters because fibroblasts, the cells that maintain connective tissue, respond to stretching and pulling. When the tissue winds around a needle, fibroblasts change shape and begin releasing signaling molecules, including adenosine triphosphate, through a process known as purinergic signaling.7PubMed Central. Anisotropic tissue motion induced by acupuncture needling along intermuscular connective tissue planes In traditional terms, the practitioner might describe this as “obtaining the qi.” In physiological terms, the needle is mechanically coupling with the tissue and initiating a chain of biochemical events.
The Deqi Sensation and Its Nerve Fibers
Practitioners and patients have long described a characteristic sensation during acupuncture called deqi, often translated as “arrival of qi.” It typically includes feelings of aching, heaviness, pressure, tingling, or warmth radiating from the needle site. A study characterizing this response found that it involves a complex pattern of sensations suggesting activation of a wide spectrum of nerve fibers, particularly the slower-conducting fibers found in muscle and tendon layers.8PubMed Central. Characterization of the “deqi” response in acupuncture These include thin myelinated fibers that carry deep aching sensations and unmyelinated fibers involved in dull pain and temperature perception.
Deqi is traditionally considered essential for therapeutic benefit. Modern imaging studies support the idea that something physiologically distinct happens when deqi occurs. Brain scans show that acupuncture stimulation associated with deqi produces a markedly different pattern of brain activity compared to needling that does not elicit the sensation, a point explored in the next section.
How the Brain Responds to Acupuncture
Functional MRI studies have revealed that acupuncture, especially when deqi is present, produces a characteristic pattern of brain activity. Regions involved in processing pain, emotion, and memory, including the amygdala, hippocampus, and prefrontal cortex, show decreased activity, while sensory and motor areas of the cortex show increased activity.9PubMed Central. The salient characteristics of the central effects of acupuncture needling: limbic-paralimbic-neocortical network modulation This pattern involves what neuroscientists call the default mode network and its anti-correlated task-positive network, two large-scale brain systems that typically operate in a push-pull fashion.10PubMed Central. Acupuncture, the limbic system, and the anticorrelated networks of the brain
A systematic review and meta-analysis of brain imaging studies confirmed that acupuncture’s effects on the brain extend well beyond simple sensory processing, encompassing regions tied to emotion, cognition, and autonomic regulation.11PLoS ONE. Characterizing Acupuncture Stimuli Using Brain Imaging with fMRI – A Systematic Review and Meta-Analysis of the Literature The deactivation of emotional and memory-related brain regions helps explain why acupuncture can reduce the distress associated with pain, even when the raw sensory intensity of the pain may not change as dramatically. Researchers have hypothesized that this broad network modulation underlies acupuncture’s effects across a range of conditions, from chronic pain and anxiety to autonomic and immune regulation.12PubMed Central. The salient characteristics of the central effects of acupuncture needling: limbic-paralimbic-neocortical network modulation
Endorphins, Adenosine, and the Chemistry of Pain Relief
The earliest modern insight into acupuncture’s pain-relieving action came from experiments showing that naloxone, a drug that blocks opioid receptors, also blocks acupuncture-induced pain relief. This directly implicated the body’s own endorphin system.13PubMed. Naloxone blockade of acupuncture analgesia: endorphin implicated Later work showed that the type of opioid released depends on stimulation frequency: low-frequency electrical acupuncture triggers the release of one class of opioid peptides in the spinal cord, while high-frequency stimulation releases a different class.14PAIN. Involvement of endogenous opioid peptides in acupuncture analgesia The overall picture includes opioids, neurotransmitters, and immune signaling molecules working at multiple levels of the nervous system.15PubMed Central. Acupuncture: Emerging evidence for its use as an analgesic (Review)
A more recently discovered pathway involves adenosine, a molecule best known for making you feel sleepy (caffeine works by blocking it). Mouse studies showed that acupuncture needle rotation at a specific point on the leg released adenosine locally, and that pain relief required adenosine A1 receptors. Blocking adenosine breakdown extended the analgesic effect.16PubMed Central. Adenosine A1 receptors mediate local anti-nociceptive effects of acupuncture A follow-up study in humans confirmed that adenosine concentration in the tissue around the needle rises during acupuncture and stays elevated for about 30 minutes afterward, but only when the needle is rotated at a recognized acupuncture point.17PubMed Central. Traditional Acupuncture Triggers a Local Increase in Adenosine in Human Subjects Inserting the needle without rotating it, or needling at a non-acupuncture location, did not produce the same adenosine spike. This finding is notable because it suggests that both point specificity and technique matter at a biochemical level, something the qi framework has insisted on for centuries.
Blood Flow, the Autonomic Nervous System, and Inflammation
Acupuncture also affects local blood circulation. Needling increases nitric oxide levels in the treated region, and this increase correlates with a rise in blood flow to surrounding tissue.18PubMed. Acupuncture enhances generation of nitric oxide and increases local circulation Electroacupuncture similarly stimulates nitric oxide release and downstream signaling that improves microcirculation at the acupuncture point.19PubMed Central. Responses of nitric oxide-cGMP release in acupuncture point to electroacupuncture in human skin in vivo using dermal microdialysis Animal experiments confirmed that nitric oxide is a major factor in the local blood flow increase from manual acupuncture.20PubMed. Contributions of nitric oxide and prostaglandins to the local increase in muscle blood flow following manual acupuncture in rats
On a systemic level, acupuncture appears to shift the balance of the autonomic nervous system toward its “rest and digest” branch. A meta-analysis found that real acupuncture increased parasympathetic tone more than placebo acupuncture, as measured by heart rate variability.21Complementary Therapies in Medicine. Acupuncture increases parasympathetic tone, modulating HRV − Systematic review and meta-analysis A separate systematic review found that acupuncture lowered markers of sympathetic dominance in people with health conditions.22PubMed Central. Effect of Acupuncture on Heart Rate Variability: A Systematic Review
Acupuncture’s anti-inflammatory potential has drawn particular interest. In a rat model of sepsis, electrical stimulation at a leg acupuncture point reduced inflammatory markers (TNF, IL-6) and improved survival. Cutting the vagus nerve or blocking catecholamine signaling eliminated the anti-inflammatory effect, revealing that the mechanism runs through specific nerve-to-adrenal-gland pathways.23PubMed Central. Electrical Stimulation at the ST36 Acupoint Protects against Sepsis Lethality and Reduces Serum TNF Levels through Vagus Nerve- and Catecholamine-Dependent Mechanisms A 2021 study published in Nature identified the specific sensory neurons in the deep leg fascia that drive this vagus-adrenal axis, adding another piece to the puzzle of why point location matters.24PubMed. Anti-inflammatory mechanism of electroacupuncture involves the modulation of multiple systems, levels and targets and is not limited to “driving the vagus-adrenal axis”
Clinical Evidence and the Sham Acupuncture Problem
The largest patient-level meta-analysis on acupuncture for chronic pain pooled data from nearly 18,000 patients in high-quality randomized trials. It found acupuncture superior to both no treatment and sham acupuncture for conditions including back pain, neck pain, osteoarthritis, and chronic headache. However, the gap between real and sham acupuncture, while statistically significant, was relatively modest, suggesting that factors beyond needle placement alone contribute to benefit.25JAMA Internal Medicine. Acupuncture for Chronic Pain: Individual Patient Data Meta-analysis
This finding has sparked ongoing debate, and much of the debate centers on what sham acupuncture actually is. The most common sham controls involve either shallow needling, needling at non-acupuncture points, or non-penetrating devices that press against the skin. The problem is that none of these are truly inert. A penetrating sham needle still activates skin and muscle nerve fibers, potentially triggering many of the same physiological cascades as “real” acupuncture.26PubMed Central. Placebo response varies between different types of sham acupuncture: A randomized double‐blind trial in neck pain patients Even non-penetrating devices involve touch, attention, and a clinical ritual, which carry their own biological effects. A systematic review of placebo acupuncture devices found that common sham tools could not reliably blind patients at sensitive acupuncture points, further complicating interpretation.27PubMed. Systematic review of acupuncture placebo devices with a focus on the credibility of blinding of healthy participants and/or acupuncturists
Recent analysis has reframed the issue by arguing that non-penetrating sham needles should be treated not as inert placebos but as active comparators that capture their own contextual and psychobiological influences.28Brain Behavior and Immunity Integrative. From sham needles to therapeutic alliance: Contextual effects in acupuncture practice Meanwhile, research into patient expectations and practitioner relationships suggests the therapeutic alliance plays a substantial role in outcomes, independent of the needle technique used.29PubMed Central. Acupuncture outcomes, expectations, patient-provider relationship, and the placebo effect: implications for health promotion In short, acupuncture consistently outperforms doing nothing, usually outperforms sham to a modest degree, and the sham itself may not be as “fake” as the trial design assumes.
Beyond Pain: Nausea and Other Applications
Acupuncture’s best-supported non-pain application is probably the prevention of nausea and vomiting, particularly from chemotherapy. Electrical stimulation at a point on the inner wrist called PC6 (Neiguan) has been studied extensively. A meta-analysis found that this stimulation reduced episodes of acute nausea and acute vomiting in cancer patients undergoing chemotherapy.30PubMed Central. Electrical Stimulation of PC 6 to Control Chemotherapy-Induced Nausea and Vomiting in Patients with Cancer: A Systematic Review and Meta-Analysis A more recent study found that a portable, noninvasive device stimulating the same point improved outcomes particularly in patients receiving highly emetogenic chemotherapy who were not receiving guideline-recommended anti-nausea drugs.31PubMed Central. Neiguan (PC6) acupoint stimulation for preventing chemotherapy-induced nausea and vomiting The anti-nausea effect appears to work through vagal nerve pathways, distinct from the opioid-based pain relief mechanisms.
Safety and Side Effects
Acupuncture performed by trained practitioners is generally safe, but it is not risk-free. A meta-analysis of prospective clinical studies estimated that at least one adverse event occurred in about 9% of patients going through a series of treatments, though the vast majority of these were minor: brief bleeding, bruising, or temporary soreness at the needle site.32BMJ Open. Acupuncture-related adverse events: systematic review and meta-analyses of prospective clinical studies Serious adverse events were rare, occurring at a rate of roughly one per 10,000 patients. Earlier prospective surveys found that the most common events were needle pain, tiredness, and minor bleeding, while pneumothorax (a collapsed lung from a needle going too deep near the chest) was exceptionally rare, occurring only twice in nearly 250,000 treatments.33PubMed. Prospective studies of the safety of acupuncture: a systematic review
The picture is different when examining case reports from the Chinese literature, which compiled 479 cases of adverse events, including 14 deaths, over several decades. The most frequent serious events included pneumothorax, fainting, bleeding into the brain lining, and infections.34PubMed Central. Acupuncture-related adverse events: a systematic review of the Chinese literature Most serious events traced back to inadequate training or poor technique, particularly needling too deeply near vital organs. Children require additional caution: acupuncture points on the top of an infant’s head should be avoided before the fontanel closes, and treatment should be adjusted for fatigue or weakness. A review of pediatric adverse events found a rate of about 1.55 events per 100 treatments, consistent with the low overall risk profile.35PubMed Central. Safety and efficacy of acupuncture in children: a review of the evidence
What Animal Studies Tell Us About Placebo
One of the persistent questions about acupuncture is how much of the benefit comes from the patient believing it will work. Animal models offer a partial answer, since you cannot easily convince a horse or a rat that they are receiving a “real” treatment. Acupuncture is used clinically in veterinary medicine, especially for pain management, and reviews of the literature describe local, spinal, and brain-level effects in animals that mirror those seen in humans: enhanced release of endogenous pain-relieving substances and reduced release of inflammatory molecules.36PubMed Central. The scientific basis of acupuncture for veterinary pain management: A review based on relevant literature from the last two decades There is also evidence from animal studies that acupuncture can promote positive changes in nervous system structure and function over time.37PubMed Central. Evidence-Based Application of Acupuncture for Pain Management in Companion Animal Medicine These findings do not eliminate the role of expectation and context in humans, but they do argue that acupuncture’s effects are not reducible to belief alone.
Cost-Effectiveness and the Economic Case
For health systems weighing whether to cover acupuncture, cost-effectiveness matters as much as clinical efficacy. An economic evaluation of acupuncture for chronic neck pain found an incremental cost-effectiveness ratio of about €12,500 per quality-adjusted life year gained, which falls well within the thresholds that most countries consider good value for a health intervention.38PubMed. Cost-effectiveness of acupuncture treatment in patients with chronic neck pain A similar analysis for chronic low back pain found acupuncture cost-effective as a complement to standard care, with the cost per disability-adjusted life year avoided becoming even more favorable when comorbid depression improved alongside pain.39PubMed. Cost-effectiveness of Acupuncture for Chronic Nonspecific Low Back Pain Acupuncture as a complete substitute for standard care was less convincing economically; the strongest case is for acupuncture added to, rather than replacing, conventional treatment.
Why the Standardization of Acupuncture Is Older Than You Think
A common assumption is that acupuncture practice was loose and variable until modern clinical standards arrived. In fact, a major standardization effort occurred during the Northern Song dynasty, roughly a thousand years ago. Wang Weiyi led the creation of an illustrated guide to acupuncture points, a proportional body-measurement method for locating points that accounted for individual variation in body size, and a life-sized bronze figure for teaching and examination. An institutional system of formulation, teaching, assessment, and feedback ensured that standards were implemented and revised over time.40Chinese Medicine and Culture. A Historical Model Informing the Future: Acupuncture Standardization in the Northern Song Dynasty The bronze figure, with drilled holes at each point that could be filled with water and covered with wax, served as a practical exam: students who needled the correct point were rewarded with a drop of water, while incorrect placement produced nothing. This system anticipated the impulse toward reproducibility and testability that modern researchers are still wrestling with today.