Understandings of acupuncture application and mechanisms

This review article offers a comprehensive analysis of the clinical applications of acupuncture and its mechanisms of action, integrating efficacy evidence with modern scientific discoveries about how this ancient therapy works in the body. Acupuncture, defined as the stimulation of specific body points through the insertion of fine needles followed by manipulation, has gained increasing recognition in Western medicine since the 1970s. The World Health Organization recommended acupuncture for 43 diseases in 1979, and a subsequent 2002 review concluded that it was effective for 28 conditions and beneficial for another 63. The most robust evidence exists for the treatment of pain, both acute and chronic.

For acute pain, high-quality randomized controlled trials have demonstrated acupuncture efficacy in postoperative pain, acute low back pain, labor pain, primary dysmenorrhea, tension-type headaches, and migraines. In emergency settings, acupuncture has proved to be as effective as intravenous morphine for acute pain, with the advantage of reducing pain 50% faster than medication in some cases, without significant adverse effects. For chronic pain conditions, the evidence is equally compelling. Acupuncture has demonstrated superior efficacy over standard care for chronic low back pain, knee osteoarthritis, chronic headaches, neck pain, and shoulder pain.

Systematic reviews and meta-analyses consistently confirm these benefits, with improvements not only in pain intensity but also in patients' function and quality of life. The mechanisms of action of acupuncture have been significantly clarified through modern biomedical technologies. At the local level of the acupoint, needle insertion activates purinergic signaling, with release of ATP that rapidly degrades into adenosine, binding to A1 receptors to mediate analgesic effects. TRPV (transient receptor potential vanilloid) channels, especially TRPV1 and TRPV2, also play a crucial role as mechanical and thermal sensors in the response to acupuncture.

Mast cell degranulation at acupoints contributes to the therapeutic effects. In the central nervous system, acupuncture modulates multiple neurotransmitters. The endorphin theory, widely accepted, explains part of the analgesic effects through activation of endogenous opioids at spinal and supraspinal levels. Additionally, acupuncture modulates serotonin and norepinephrine at the spinal level, and recent studies have identified an orexin-endocannabinoid pathway in the periaqueductal gray that contributes to non-opioid analgesia.

For anti-inflammatory effects, acupuncture acts on the hypothalamic-pituitary-adrenal axis, reducing COX-2 and PGE2 levels, in addition to stimulating the release of catecholamines from the adrenal gland that act on D1 dopaminergic receptors for systemic anti-inflammatory effects. In other applications, the evidence is less conclusive. For insomnia, although acupuncture is widely used clinically, systematic reviews indicate marginal benefits, with a need for higher-quality studies. The proposed mechanism involves inhibition of sympathetic activity and modulation of the hypothalamic-pituitary-adrenal axis.

For substance dependence, particularly opioids, auricular acupuncture has been used since 1972, but only a few randomized controlled studies of adequate quality have been conducted. The mechanism involves modulation of dopamine release in the nucleus accumbens, reducing the positive and negative reinforcement effects of drugs. Recent studies show that electroacupuncture can prevent relapse to cocaine use by reducing the expression of ΔFosB and GluR2 in the nucleus accumbens. For other conditions such as stroke, in vitro fertilization, and various diseases, more high-quality studies are needed to definitively establish efficacy.

Methodological challenges specific to acupuncture studies include difficulties in adequate blinding and design of appropriate control groups. The question of acupoint specificity remains important, with evidence suggesting that stimulation at real points is superior to stimulation at non-therapeutic points. The future of acupuncture research promises significant advances with innovative technologies such as "i-needles," which allow metagenomic and metatranscriptomic analysis, and implantable microsensors that can monitor microenvironmental changes in real time at acupoints and target organs. These technologies may accelerate our understanding of the mechanisms of action of acupuncture and identify biomarkers associated with its therapeutic effects.