Most people walk out of an acupuncture session feeling relaxed and a little tired, and the most common physical aftereffects are mild: slight soreness at the needle sites, small bruises, and a wave of fatigue that can last hours or, occasionally, a day or two. One study tracking nearly 1,300 acupuncture treatments found that roughly a quarter of participants reported tiredness after their sessions, while smaller numbers noticed feeling cold, dizzy, or sweaty.1PubMed. Type and frequency of side effects during PC6 acupuncture: observations from therapists and patients participating in clinical efficacy trials of acupuncture Serious complications are vanishingly rare. What follows is a closer look at the full range of reactions your body can have, from the benign to the unusual.
The Most Common Side Effects
A large evidence mapping that pulled together data from 535 systematic reviews offers one of the most comprehensive pictures of acupuncture side effects available. The most frequently reported issues were pain at the needle site, bleeding or bruising, and hematoma (a deeper pocket of blood under the skin that can leave a blue-purple mark). Other effects showed up less often: headache, itching, redness, minor swelling, numbness, and temporary worsening of the original symptoms.2PubMed Central. Adverse effects associated with acupuncture therapies: An evidence mapping from 535 systematic reviews
Bleeding at the needle site is especially common simply because tiny capillaries sit just beneath the skin, and even a skilled practitioner can nick one. In those cases, a bit of pressure with a cotton swab is all that is needed. Bruising and small hematomas typically resolve on their own within a few days to a week without any treatment.2PubMed Central. Adverse effects associated with acupuncture therapies: An evidence mapping from 535 systematic reviews A trial comparing electroacupuncture and manual acupuncture for knee osteoarthritis recorded 25 minor adverse events across both groups, mostly hematomas and some lingering needle-site soreness, all of which went away within a week on their own.3Journal of Pain Research. Effect of Electro-Acupuncture (EA) and Manual Acupuncture (MA) on Markers of Inflammation in Knee Osteoarthritis
Fatigue deserves special mention because it catches people off guard. You may have gone in feeling relatively alert and come out wanting a nap. In the PC6 acupuncture study mentioned earlier, tiredness was the single most reported post-treatment side effect at about 26% of participants per week. Feeling cold (about 18%) and dizziness (about 10%) were next in line.1PubMed. Type and frequency of side effects during PC6 acupuncture: observations from therapists and patients participating in clinical efficacy trials of acupuncture These are not signs that something went wrong. They are part of your nervous system recalibrating, which brings us to what is actually happening inside your body during and after a session.
Why You Feel Relaxed, Tired, or Spacey Afterward
Acupuncture shifts the balance of your autonomic nervous system, the part that controls heart rate, digestion, and stress responses, toward what is sometimes called “rest and digest” mode. A systematic review and meta-analysis found that real acupuncture increases parasympathetic (calming) nervous system activity compared to sham acupuncture, as measured by changes in heart rate variability.4Complementary Therapies in Medicine. Acupuncture increases parasympathetic tone, modulating HRV − Systematic review and meta-analysis A more recent study showed that acupuncture at certain points activates the vagus nerve in real time, and that this enhanced calming activity can persist for five to ten minutes after the needles come out.5PubMed Central. Regulation of autonomic nervous system by acupuncture: a heart rate variability study on physical stress
At the tissue level, the needle does more than just sit there. Manipulating it generates mechanical force that travels through collagen fibers in the connective tissue and activates mast cells, a type of immune cell packed densely around acupuncture points. Those mast cells release histamine, serotonin, and adenosine into the surrounding space, which then trigger nearby nerve endings.6PubMed Central. Activation of Subcutaneous Mast Cells in Acupuncture Points Triggers Analgesia Beyond these local signals, acupuncture also prompts the release of the body’s own opioid-like chemicals, including endorphins and enkephalins, as well as compounds like oxytocin. At one commonly used leg point, researchers measured elevated adenosine concentrations that lasted more than an hour after treatment.7International Journal of Complementary & Alternative Medicine. Biomedical Effects of Acupuncture
So the post-session drowsiness and calm are not mysterious. Your vagus nerve has been dialed up, your body is circulating its own painkillers, and your sympathetic (“fight or flight”) system has taken a back seat. For most people this feels pleasant. For some, it can feel briefly disorienting.
The De Qi Sensation
During a session, you may feel something called “de qi” (pronounced roughly “duh chee”), a distinctive sensation at or around the needle site that practitioners consider a sign the treatment is working. People describe it as a dull ache, heaviness, warmth, tingling, or a spreading pressure that radiates outward from the needle. It is not sharp pain, which would indicate a problem.
Brain imaging has helped confirm that de qi is a real neurological event, not just suggestion. A study using SPECT scans found that when participants experienced de qi, a distinct pattern of brain activation appeared, including areas involved in sensory integration, emotion, and motor planning. When participants felt nothing at the needle, those same regions stayed quiet.8PubMed. Brain areas involved in acupuncture needling sensation of de qi: a single-photon emission computed tomography (SPECT) study Not everyone experiences de qi during every session, and its intensity can vary depending on the point used, the practitioner’s technique, and individual sensitivity.
Vasovagal Responses
A small number of people experience a vasovagal response during or shortly after acupuncture, which is the same fainting-type reaction some people get during blood draws. The vagus nerve fires excessively, causing a sudden drop in heart rate and blood pressure. Symptoms can include dizziness, nausea, sweating, feeling lightheaded, and in uncommon cases, actually passing out. Estimates of how often this happens range widely, from about 0.02% to 7% of treatments, depending on the study and how broadly the researchers defined the response.9PubMed Central. Acupuncture-Associated Vasovagal Response: Revised Terminology and Hospital Experience
Vasovagal episodes are more likely if you are dehydrated, have not eaten, are anxious, or are having acupuncture for the first time. The fix is straightforward: lying down, drinking water, and waiting for the episode to pass. Practitioners watch for warning signs and will remove needles immediately if one begins. If you have a history of fainting during medical procedures, let your acupuncturist know beforehand.
Rare but Serious Complications
Serious adverse events from acupuncture are genuinely rare. The best estimate puts them at roughly 0.05 per 10,000 treatments.10PubMed Central. Navigating the Needles: Unveiling the Risks of Acupuncture: A Case Report When they do occur, the most reported serious complications are internal organ injuries and infections. A Japanese analysis of adverse event reports found that internal injuries accounted for about a third of reported serious events, and infections made up about a fifth.11PubMed Central. Analysis of Adverse Events in Acupuncture and Moxibustion Treatments in Japan and the Current Situation of Hiroshima University Hospital Kampo Clinical Center
Pneumothorax, a collapsed or partially collapsed lung caused by a needle puncturing the chest wall, is the most discussed serious complication in the literature. It happens when needles are inserted too deeply or at the wrong angle near the upper back, shoulders, or chest. The risk is tied overwhelmingly to practitioner error, particularly improper depth, angle, or point selection. Research from China found that these events were concentrated in community clinics with less-trained practitioners, not in hospitals or established acupuncture practices.12Acupuncture & Electro-Therapeutics Research. Risk Analysis of Pneumothorax Caused by Acupuncture and its Prevention and Control
Infection risk has changed dramatically over the decades. An older era of acupuncture complications was dominated by hepatitis transmission from reusable needles. A systematic review of case reports found that in more recent data, the pattern shifted: the majority of infections are now bacterial and caused by inadequate skin hygiene at the needle site rather than by contaminated needles.13PubMed Central. Adverse Events of Acupuncture: A Systematic Review of Case Reports The widespread adoption of single-use, sterile, disposable needles and clean needle technique protocols has virtually eliminated the old hepatitis risk. If your practitioner is using anything other than single-use needles from a sealed package, that is a red flag.
How Your Expectations Affect What You Feel
Your mindset going into a session genuinely shapes what you experience afterward, and this is not just a vague “power of positive thinking” claim. A study of cancer patients receiving either real or sham acupuncture found that 79% of patients who strongly believed acupuncture would work reported positive side effects, compared to 0% of patients who did not believe it would help. The same study found that certain factors predicted a nocebo response (feeling worse): being younger, being female, and experiencing pain from the needles themselves were all associated with more negative side effects.14PubMed Central. Understanding Placebo and Nocebo Responses Based on a Randomized Sham-Controlled Study on Acupuncture in Integrative Cancer Care
A separate trial tested whether giving patients a more intense warning about possible side effects before treatment changed their actual experience. Patients who received the detailed adverse-effect briefing reported somewhat more side effects afterward compared to those who received a standard briefing, though the difference did not reach statistical significance.15JAMA Network Open. Effect of Briefing on Acupuncture Treatment Outcome Expectations, Pain, and Adverse Side Effects Among Patients With Chronic Low Back Pain The takeaway is practical: if you are nervous or bracing for a bad experience, you are more likely to notice and report discomfort. Going in calm and reasonably informed, without catastrophizing, is genuinely helpful.
If You Take Blood Thinners
People on anticoagulants like warfarin or antiplatelet medications often worry that acupuncture will cause excessive bleeding. The evidence is reassuring. A systematic review of acupuncture in anticoagulated patients found that across nearly 4,000 treatments, only one moderate bleeding event occurred, a large hip hematoma that required medical management. Blood-spot bleeding, the kind easily controlled with a bit of pressure, happened in about 15% of treatments in one case series, which is not far off the rate you would see with any needle stick.16PubMed Central. Acupuncture Safety in Patients Receiving Anticoagulants: A Systematic Review
A study directly comparing acupuncture patients on warfarin to those not on blood thinners found that bruising rates were similar across groups, ranging from about 1% to 2%. Microbleeding, which stopped within 10 to 20 seconds in the vast majority of cases, ran between about 1% and 5% regardless of anticoagulation status. No extensive bleeding or hemorrhage was observed in any group.17PubMed Central. Does acupuncture increase the risk of bleeding in patients taking warfarin? A separate retrospective review of over 4,800 treatments in patients on warfarin or antiplatelet medications confirmed these findings: no serious adverse events occurred, and microbleeding stopped within 30 seconds.18European Journal of Integrative Medicine. Safety of acupuncture treatments for patients taking warfarin or antiplatelet medications: Retrospective chart review study You should still tell your acupuncturist about your medications so they can adjust technique and needle depth, but being on blood thinners is not a reason to skip acupuncture.
Acupuncture During Pregnancy
Pregnant women considering acupuncture often hear conflicting advice. A systematic review that assessed safety across 105 studies found the overall adverse event rate was about 1.9%, and when researchers narrowed that down to events they judged were actually caused by the acupuncture itself, the rate dropped to 1.3%. All of these causally related events were mild to moderate in severity, with needling pain being the most common. Severe adverse events and deaths were few and, in the researchers’ assessment, all considered unlikely to have been caused by the acupuncture.19PubMed Central. The safety of acupuncture during pregnancy: a systematic review
That said, certain acupuncture points are traditionally avoided during pregnancy because they are believed to stimulate uterine contractions. A trained practitioner who knows you are pregnant will avoid those points and adjust your positioning so you are comfortable. The evidence does not suggest that acupuncture in the hands of a qualified practitioner poses meaningful risk during pregnancy, but full disclosure about your trimester and any pregnancy complications is essential.
How Effects Build Over Multiple Sessions
If you are getting acupuncture for chronic pain, a single session is unlikely to produce lasting results. The question of dosing, how many sessions, how often, and for how long, turns out to matter a lot. A review of randomized trials found that the rate of pain relief stayed above 20% for up to about 18 weeks after a course of treatment, and then dropped sharply below 10% as follow-up extended further.20PubMed Central. What Is the Appropriate Acupuncture Treatment Schedule for Chronic Pain? Review and Analysis of Randomized Controlled Trials
Clinical trials have tested various treatment schedules, from once a week to five times a week, over periods ranging from four to twelve weeks. The findings suggest that too little acupuncture may not work at all: one trial found that fewer than one session per week over twelve weeks did not improve chronic knee pain. But sessions given about twice a week for eight weeks did produce meaningful improvements for osteoarthritis of the knee. For chronic low back pain, a regimen of ten sessions delivered twice weekly showed significant pain relief, though the advantage over sham acupuncture was modest.21PubMed Central. Establishing an adequate dose of acupuncture is essential for clinical trial studies The general picture is that acupuncture works cumulatively: expect gradual improvement over a course of treatment rather than a dramatic shift after one visit.
What Happens in Your Brain
One of the more interesting lines of acupuncture research involves brain imaging. Several studies have used functional MRI and other scanning techniques to look at how acupuncture changes connectivity patterns in the brain’s default mode network, the set of regions active when you are daydreaming, mind-wandering, or not focused on a specific task. This network is often disrupted in chronic pain conditions.
In chronic migraine patients, researchers found that acupuncture treatment restored connectivity in certain default mode network regions to levels seen in healthy people. Specifically, areas in the prefrontal cortex and precuneus that had weakened connections in migraine patients showed increased connectivity after a course of acupuncture, and these changes tracked alongside reductions in migraine symptoms.22PubMed Central. Acupuncture Reversible Effects on Altered Default Mode Network of Chronic Migraine Accompanied with Clinical Symptom Relief A separate study looked at what happens to brain connectivity during and immediately after needle insertion. It found that acupuncture altered the communication between the posterior cingulate cortex and the cerebellum, and between the angular gyrus and the frontal cortex, both during needle retention and after needle removal.23PubMed Central. Immediate and sustained effects of acupuncture on the default mode network
These brain-level findings are still being mapped and interpreted, and no one is yet claiming that a single session rewires your brain in any lasting way. But they do offer a plausible explanation for why acupuncture can leave people feeling mentally “different” afterward, whether that is a sense of calm, a spacey quality, or a shift in how pain registers. Your brain is not just passively receiving signals from the needles; it is actively reorganizing how certain regions talk to each other, at least temporarily. That neurological reshuffling, combined with all the chemical and nervous system changes happening at the same time, is what adds up to the post-acupuncture experience most people describe as something between deep relaxation and pleasant disorientation.