5 Studies that Show How Acupuncture Works

Acupuncture Research

What Brain Imaging, Nerve Conduction Testing, and Laboratory Research Have Measured When an Acupuncture Needle Is Placed in the Body

"How does acupuncture actually work?" is one of the most common questions we hear in clinic. For most of its history, acupuncture was explained in traditional language that does not map neatly onto modern anatomy and physiology, which leaves many people unsure whether anything measurable is happening at all. Researchers have tested that question directly. These are the five studies we think answer it best.

Key Points

• Acupuncture produces measurable changes in the brain, the nerves, and the tissue around the needle. It can be described in terms of physiology without relying on traditional concepts.
• In a PET imaging trial of people with fibromyalgia, acupuncture increased mu-opioid receptor availability in pain-processing regions of the brain. Sham acupuncture did not (Harris et al., 2009).
• In a trial of 80 people with carpal tunnel syndrome, real and sham acupuncture both reduced symptoms, but only real acupuncture improved median nerve conduction and brain mapping of the fingers (Maeda et al., 2017).
• Laboratory studies in mice have identified two specific pathways: adenosine release at the needle site (Goldman et al., 2010) and a nerve circuit from the leg that may reduce body-wide inflammation (Liu et al., 2021).
• In healthy adults, needling into muscle increased local muscle blood flow for 20 minutes, while a shallow insertion did not (Sandberg et al., 2003).
• These studies explain how acupuncture may work. They do not show that it works for every condition.

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How We Chose These Five Studies

We looked for studies that measured something objective, were published in respected peer-reviewed journals, and did not rely on traditional concepts to make their case. Three are human trials and two are laboratory studies in mice.

Each one looks at a different part of the picture: brain chemistry, nerve function, local tissue, the autonomic nervous system, and circulation. Together they cover the main ways acupuncture affects the body.

Five Studies at a Glance

Study	Subjects	What Was Measured	Main Finding
Harris et al., 2009 NeuroImage	People with fibromyalgia	Opioid receptors in the brain (PET imaging)	Acupuncture increased receptor availability; sham did not
Maeda et al., 2017 Brain	80 people with carpal tunnel syndrome	Nerve conduction and brain mapping (fMRI)	Real acupuncture improved both; sham improved symptoms only
Goldman et al., 2010 Nature Neuroscience	Mice	Chemicals released near the needle	Adenosine release was required for pain relief
Liu et al., 2021 Nature	Mice	Sensory nerves and inflammation	A specific nerve pathway from the leg reduced inflammation
Sandberg et al., 2003 European Journal of Applied Physiology	14 healthy women	Skin and muscle blood flow	Needling into muscle increased local blood flow

1. Acupuncture Changes Opioid Receptor Activity in the Brain

Harris et al., 2009 · NeuroImage

The body has its own pain-relieving system built around opioid receptors in the brain. Researchers at the University of Michigan wanted to know whether acupuncture acts on that system differently than a placebo does.

What They Did

People with fibromyalgia were randomly assigned to traditional acupuncture or sham acupuncture over four weeks. The team used PET imaging to measure mu-opioid receptor availability during the first session and again after the eighth treatment.

What They Found

Acupuncture increased mu-opioid receptor availability in several pain-processing regions of the brain, including the cingulate, insula, caudate, thalamus, and amygdala (Harris et al., 2009).

• The increases appeared during the first session.
• They were still present in some of the same regions after a month of treatment.
• The sham group did not show these increases. It showed small reductions instead.
• Larger long-term increases were associated with greater reductions in clinical pain.

Why It Matters

This study suggests that acupuncture and sham acupuncture may act on the brain's opioid system in different ways, even when patients in both groups report feeling better. It is one of the clearest human examples of how acupuncture may relieve pain through the central nervous system.

RelatedUnderstanding Acupuncture for Analgesia RelatedReviewing the Pathophysiology of Chronic Pain

2. Acupuncture Improves Nerve Function and Brain Mapping in Carpal Tunnel Syndrome

Maeda et al., 2017 · Brain

Carpal tunnel syndrome is useful for research because it can be measured objectively. A nerve conduction test shows how well the median nerve is working at the wrist, regardless of how the patient says they feel.

What They Did

Researchers at Massachusetts General Hospital enrolled 80 people with carpal tunnel syndrome and divided them into three groups:

• Electroacupuncture at the affected wrist and hand
• Electroacupuncture at a distant site near the opposite ankle
• Sham electroacupuncture using placebo needles that did not penetrate the skin

Each group received 16 sessions over 8 weeks. The team measured symptoms, median nerve conduction, and how the fingers were represented in the brain's primary somatosensory cortex using functional MRI.

What They Found

All three groups reported fewer symptoms. The objective results were different. Only the real acupuncture groups improved on the physiological measures (Maeda et al., 2017).

• Median nerve conduction at the wrist improved.
• The brain's map of the index and middle fingers improved.
• Patients with greater improvement in that brain map were more likely to still feel better three months later.

Why It Matters

Sham treatment made people feel better in the short term. Real acupuncture was also associated with measurable changes in the nerve and the brain, and those changes predicted longer-lasting relief.

RelatedCarpal Tunnel Treatment NYC RelatedDry Needling for Carpal Tunnel Syndrome

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3. Acupuncture Releases Adenosine at the Needle Site

Goldman et al., 2010 · Nature Neuroscience

The first two studies looked at the brain. This one looked at what happens in the tissue right around the needle.

What They Did

A team at the University of Rochester Medical Center studied acupuncture in mouse models of pain. They measured the chemicals released in the tissue near the needle, then tested whether blocking or boosting those chemicals changed the pain relief.

What They Found

Acupuncture triggered a local release of adenosine, a natural compound with pain-relieving properties (Goldman et al., 2010).

• The pain relief depended on the adenosine A1 receptor. Without that receptor, acupuncture did not reduce pain.
• Injecting a drug that activates the A1 receptor reproduced the pain-relieving effect of acupuncture.
• Slowing the breakdown of adenosine increased both the adenosine level and the pain relief.

Why It Matters

This study identified a specific local mechanism: the needle causes tissue to release adenosine, and adenosine quiets nearby pain signaling. It offers a plausible explanation for why needling close to a painful area may help.

This was an animal study, so the findings cannot be applied directly to people. It is included here because it identified a precise chemical pathway, tested it from several directions, and was published in one of the leading neuroscience journals.

4. Electroacupuncture Activates a Nerve Pathway That May Reduce Inflammation

Liu et al., 2021 · Nature

One of the oldest questions about acupuncture is whether it matters where the needle goes. This study from Harvard Medical School gave an anatomical answer for one specific pathway.

What They Did

Researchers applied low-intensity electroacupuncture to mice at a point on the hindlimb that corresponds to ST36, and compared it with a point on the abdomen. They then traced which sensory nerves were responsible for the effects.

What They Found

Stimulation at the hindlimb point activated a specific set of sensory neurons in the deep tissue of the leg (Liu et al., 2021).

• Those neurons signaled the brainstem, which activated the vagus nerve and the adrenal glands.
• This reduced body-wide inflammation caused by a bacterial toxin.
• When the researchers removed those specific neurons, the anti-inflammatory effect disappeared.
• The same low-intensity stimulation on the abdomen did not activate this pathway, because those neurons are not found in the abdominal tissue.

Why It Matters

The study showed that, at least for this pathway, needle location matters for an anatomical reason. The effect depends on which nerve fibers are present in the tissue being stimulated.

This was also a mouse study, and it used electrical stimulation. It supports the broader idea that acupuncture may influence inflammation through the autonomic nervous system.

RelatedUnderstanding Acupuncture's Anti-Inflammatory Effects RelatedPain and the Immune System

5. Needling Into Muscle Increases Local Blood Flow

Sandberg et al., 2003 · European Journal of Applied Physiology

Patients often ask whether acupuncture improves circulation. This Swedish study measured it directly.

What They Did

Fourteen healthy women received needling over the front of the shin on separate days, in random order:

• A shallow insertion into the skin
• An insertion into the tibialis anterior muscle
• An insertion into the muscle with the needle manipulated until the person felt a distinct heaviness, fullness, or numbness
• A control session with no needle

The researchers recorded skin and muscle blood flow before the needle went in and for 20 minutes afterward.

What They Found

Needling into the muscle increased muscle blood flow for the full 20 minutes compared with the control session (Sandberg et al., 2003).

• The increase was largest in the first 5 minutes when the needle was manipulated.
• Skin blood flow also rose for 5 minutes after the manipulated insertion.
• The shallow insertion did not increase blood flow.

Why It Matters

The study suggests that depth and intensity of needling affect the circulatory response. A shallow needle and a needle placed and stimulated in muscle do not appear to do the same thing.

It was a small study in healthy volunteers, and the authors noted that anxiety before the stronger stimulation may have influenced the skin results. It still helps explain why technique is an important part of treatment for myofascial pain.

RelatedHow Does Dry Needling Work? Try NowTrigger Point Pain Finder

What These Five Studies Add Up To

No single study explains acupuncture. Read together, these five describe a treatment that acts at several levels of the body at once. In plain terms, the research suggests acupuncture may:

• Engage the brain's own pain-relieving chemistry
• Improve how nerves conduct signals and how the brain maps the body
• Release pain-relieving compounds in the tissue around the needle
• Activate nerve reflexes that influence inflammation
• Increase blood flow in the muscle being treated

A needle stimulates nerves, changes local tissue chemistry and blood flow, and sends signals to the spinal cord and brain. Those signals may change how pain is processed and how the body regulates inflammation.

What These Studies Do Not Show

It is important to be clear about the limits.

• Two of the five are mouse studies. Animal findings do not always carry over to people.
• Several are small. The blood flow study included 14 healthy volunteers.
• Two used electroacupuncture, which adds electrical stimulation to the needles.
• A mechanism is not the same as a clinical result. These studies explain how acupuncture may work, not how well it works for a given condition.

For questions about results, clinical trials and reviews are the better source. Our summaries of the research on acupuncture for musculoskeletal pain and acupuncture for low back pain are good places to start.

The research is still developing, and it does not support every claim made about acupuncture. It does show that something real and measurable happens when a needle is placed in the body.

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Frequently Asked Questions

Is acupuncture just a placebo?

The studies above suggest it is more than that. In the fibromyalgia and carpal tunnel trials, people who received sham acupuncture also reported feeling better, but only real acupuncture was associated with changes in opioid receptors, nerve conduction, and brain mapping. Expectation and context still matter, as they do with any treatment.

Does it matter where the needles go?

For some effects, it appears to. In the 2021 Nature study, stimulation on the leg activated an anti-inflammatory nerve pathway that the same stimulation on the abdomen did not. In the carpal tunnel trial, needling near the wrist and needling near the opposite ankle both improved nerve function, but appeared to involve different areas of the brain.

Does needle depth matter?

It may. In the blood flow study, a shallow insertion did not change circulation, while needling into the muscle did.

Does acupuncture release endorphins?

Acupuncture appears to engage the body's opioid system. The PET study showed changes in mu-opioid receptors, which are the receptors that endorphins and similar compounds act on.

Do these findings apply to dry needling?

Dry needling is a needling technique that uses acupuncture needles to treat trigger points in muscle. These five studies tested acupuncture and electroacupuncture, so the results should not be assumed to carry over in full. The blood flow study is the most relevant, since it measured what happens when a needle is placed in muscle. You can read more in How Does Dry Needling Work?

How many sessions does it take to see these effects?

It varies. Some changes were measured during or right after a single session. Others, such as the nerve and brain changes in the carpal tunnel trial, were measured after 16 sessions over 8 weeks. Your practitioner can give you a realistic estimate at your first visit.

References

1. Goldman, N., Chen, M., Fujita, T., Xu, Q., Peng, W., Liu, W., Jensen, T. K., Pei, Y., Wang, F., Han, X., Chen, J. F., Schnermann, J., Takano, T., Bekar, L., Tieu, K., & Nedergaard, M. (2010). Adenosine A1 receptors mediate local anti-nociceptive effects of acupuncture. Nature Neuroscience, 13(7), 883-888. https://doi.org/10.1038/nn.2562 | https://pubmed.ncbi.nlm.nih.gov/20512135/
2. Harris, R. E., Zubieta, J. K., Scott, D. J., Napadow, V., Gracely, R. H., & Clauw, D. J. (2009). Traditional Chinese acupuncture and placebo (sham) acupuncture are differentiated by their effects on mu-opioid receptors (MORs). NeuroImage, 47(3), 1077-1085. https://doi.org/10.1016/j.neuroimage.2009.05.083 | https://pubmed.ncbi.nlm.nih.gov/19501658/
3. Liu, S., Wang, Z., Su, Y., Qi, L., Yang, W., Fu, M., Jing, X., Wang, Y., & Ma, Q. (2021). A neuroanatomical basis for electroacupuncture to drive the vagal-adrenal axis. Nature, 598(7882), 641-645. https://doi.org/10.1038/s41586-021-04001-4 | https://pubmed.ncbi.nlm.nih.gov/34646018/
4. Maeda, Y., Kim, H., Kettner, N., Kim, J., Cina, S., Malatesta, C., Gerber, J., McManus, C., Ong-Sutherland, R., Mezzacappa, P., Libby, A., Mawla, I., Morse, L. R., Kaptchuk, T. J., Audette, J., & Napadow, V. (2017). Rewiring the primary somatosensory cortex in carpal tunnel syndrome with acupuncture. Brain, 140(4), 914-927. https://doi.org/10.1093/brain/awx015 | https://pubmed.ncbi.nlm.nih.gov/28334999/
5. Sandberg, M., Lundeberg, T., Lindberg, L. G., & Gerdle, B. (2003). Effects of acupuncture on skin and muscle blood flow in healthy subjects. European Journal of Applied Physiology, 90(1-2), 114-119. https://doi.org/10.1007/s00421-003-0825-3 | https://pubmed.ncbi.nlm.nih.gov/12827364/

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