Yes, it is generally very safe and has no side effects, though minor adverse events may happen, such as needle caused sharp pain, which disappears soon after adjustment. The acupuncturist in Kapiti always listens to you and follows sound procedures and takes care of the minor discomfort.
Zhang et al 2010 (Review of 98 case reports and 17 case series)(1) ‘Various types of acupuncture-related adverse events have been reported in China. Similar events have been reported by other countries, usually as a result of inappropriate technique. Acupuncture can be considered inherently safe in the hands of well-trained practitioners’ (1).
The short answer is: the Qi-mechanism of acupuncture, when needles inserted into human body's channel network. Pain and discomfort, by Chinese definition, is a disruption of the channel pathway. The intervention of a needle into an affected channel is to invigorate and quicken the Qi and Blood flow in the affected channel(s). The ancient Chinese saying: "Bu tong ze tong (不通则痛),"can be literally translated to: "when there is a stagnation of Qi flow, there is pain and discomfort." the purpose of using needles is to achieve "tong ze bu tong (通则不痛),“ which means whenever the Qi flow has been restored, there is no pain".
It has been proved hard for modern science when it comes to understand how does acupuncture work. Which is reasonable, as the modern science exams and looks for tangible and structural changes of a health condition or an intervention, it focuses on visible and quantitative measurable results. Acupuncture has a focus on the big and holistic picture of human body. The closest match in modern scientific thoughts is by integrating concepts of multiple theories such as embryology, pathomorphology, neurology, cosmology, and more...
Advanced modern technologies, such as functional magnetic resonance imaging (fMRI) scan, in a 2010 exploration, has revealed emerging neuroscience evidence. The revealed changes took place in larger and multiple areas of the brain to specific true acupuncture points, by needling which has built up a two way neuro-biological reaction that 'needle stimulation inhibited incoming noxious stimuli with a peripheral-central bottom up somatosensory modulation (2).
Difference between true and placebo needles: 'both genuine and sham acupuncture equally reduced noxious stimuli' but in a different biological reaction that 'needle stimulation inhibited incoming noxious stimuli with a peripheral-central bottom up somatosensory modulation while sham acupuncture activated a top-down modulation of pain and worked through the brain’s emotional circuitry'(2). The revelation has clarified two things:
1. Zhang J, Shang H, Gao X, Ernst E. Acupuncture-related adverse events: a systematic review of the Chinese literature. Bulletin of the World Health Organization. [Review]. 2010 Dec 1;88(12):915-21C. [PubMed]
2. Kaptchuk TJ, Chen K, Song J. Recent clinical trials of acupuncture in the west: Responses from the practitioners. Chin J Integr Med [Internet]. 2010 Jun 8 [cited 2017 Aug 20];16(3):197–203. Available from: http://www.ncbi.nlm.nih.gov/pubmed/20694771