A Literature Review on the Physiological Processes of Acupuncture

The needle goes in. The pain, sometimes, recedes. And at once an irresistible question rises: by what mechanism? Our era likes to explain; it distrusts what it can’t situate within a circuit. Yet in medicine the path of proof rarely runs from mechanism towards effect: it most often starts from the effect, observed and measured, and then works back towards the mechanism we try to reconstruct. Acupuncture offers a textbook case of this tension.

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The trap of explanation

A plausible mechanism is seductive; it reassures, it “sounds scientific.” But on its own it proves nothing. The history of medicine is full of treatments that worked long before anyone knew why: aspirin relieved generations before its mode of action was understood. And the reverse exists too: fine mechanistic stories sometimes accompany therapies with no real effect. This is why two questions that are readily confused must be kept apart: what the needle sets off in the body, and whether a treatment helps, or doesn’t, the person consulting.

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What mechanistic research has found, and its status

There’s no shortage of leads. They operate at different levels (local, peripheral, central) and in all likelihood combine. Here are the main ones, each time with its degree of solidity.

• Endogenous opioids. This is the oldest hypothesis: in animals, the analgesia produced by acupuncture is partly lifted by naloxone (an opioid antagonist), which points towards the release of endorphins and enkephalins. Robust in the laboratory; harder to isolate in humans.
• Adenosine. At the puncture site itself, acupuncture raises the local level of adenosine, which acts on A1 receptors; in mice lacking this receptor, the pain-relieving effect disappears (Goldman, Nedergaard et al., 2010). A precise local mechanism, demonstrated in mice.
• The autonomic nervous system. Stimulation can tip the balance towards the parasympathetic side (the recovery side), lowering certain stress markers. Plausible and measured in a few studies.
• Connective tissue. The needle “catches” connective tissue and its rotation remodels it locally; Langevin and Yandow noted, in anatomical sections of the arm, a correspondence of about 80% between the points and the planes of connective tissue (Anatomical Record, 2002). An elegant anatomical hypothesis: a single study, never replicated.
• Brain networks. Imaging (fMRI) suggests that acupuncture modulates certain brain networks, among them the default mode network. Suggestive, not conclusive.

None of these leads “is” the explanation on its own. Above all, most are established in animals or through imaging: so many clues about the how, which don’t, by themselves, amount to a demonstration of benefit for the patient.

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But a mechanism is not a proof

A mechanism explains how a thing might act; only a clinical trial says whether it acts, and to what extent. The real question therefore shifts from the laboratory bench to the patient’s bedside: no longer “what does the needle set off?” but “is the person treated better off, and by how much?” That second question has traps of its own, which we set out in Does acupuncture work? An honest answer.

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What the clinical evidence says

For chronic pain, we have a weighty reference. An individual patient data meta-analysis (Vickers et al., 2018) pooled 39 trials and 20,827 patients (headache and migraine, osteoarthritis, low back pain, neck pain, shoulder pain). Its authors report that acupuncture did better than a no-acupuncture control group and than sham acupuncture, and that the effect persists over time. The magnitude can be stated: about 0.2 standard deviations against sham acupuncture, about 0.5 against a no-acupuncture control, a group that most often received usual care or waited its turn rather than nothing at all, with persistence at one year that decays by roughly 15%. That’s what “modest” means here. This is a research finding, presented as such, and not a promise.

The honest synthesis holds in one sentence: for chronic pain, a real but modest clinical effect; plausible but unsettled mechanisms; and two questions — the how and the how much — that must not be confused.

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And what about Qi in all this?

The classical reading speaks of regulating the Qi along the meridians. This is the grammar within which the practice was conceived and transmitted: a map, an inherited theoretical framework, neither a measured mechanism nor a piece of clinical evidence. The biomedical hypotheses don’t “validate” this vocabulary; they cast the same acts in a different light.

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Why two people don’t receive the same treatment

This grammar has a very concrete consequence in the treatment room. Two people consulting for a similar pain rarely leave with the same points. Where the pain sits, its quality, the movements that make it worse, sleep, stress, the overall picture: all of it guides the choice of points and techniques. There’s no fixed recipe to apply, only a stimulation to adjust to what is observed. One more reason to read the average effect of a meta-analysis for what it is: an average, which describes no one exactly.

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In practice

At the clinic, in the Plateau-Mont-Royal, acupuncture is offered as a complement to your medical care, never in its place and with no promise of results. The first session lasts 75 to 90 minutes, follow-ups 60 to 70 minutes, depending on the practitioner. For an overview of the evidence by indication, see our survey of the research; and our essay on effectiveness and medicine. To book: monacupuncteur.janeapp.com. In clinic: reasons for consulting.

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Read also: The black box is everywhere.

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Sources

• Vickers AJ et al. (2018). Acupuncture for Chronic Pain: Update of an Individual Patient Data Meta-Analysis. J Pain. Consult ↗
• Goldman N, Nedergaard M et al. (2010). Adenosine A1 receptors mediate local anti-nociceptive effects of acupuncture. Nature Neuroscience. Consult ↗
• Langevin HM, Yandow JA (2002). Relationship of acupuncture points and meridians to connective tissue planes. The Anatomical Record. Consult ↗