If adverse effects are understood as "something that happened unexpectedly" while receiving drug treatment, there is no difference between adverse effects and complications. However, acupuncture is a process different from the use of drugs. While acupuncture procedures should not be taken for granted as safe, complications causing harm are usually, according to the authors, the result of negligence, and should be differentiated from other adverse effects. Harmful complications noted consisted of bleeding and damage to the tissues and organs under the puncture sites. Adverse effects consisted of symptomatology like fainting and other systemic disturbances difficult to explain. In a study of acupuncture complications and adverse effects in 2000 procedures conducted by experienced professional acupuncturists in a research institution, it was found that complications did not occur, and adverse events happened infrequently. Attempts were made to explain the causes of adverse effects. Now that acupuncture is being widely incorporated into medical practice, a good understanding of adverse effects and complications would be necessary and helpful.