When performed by a trained professional, acupuncture is usually safe, however, there are a few possible hazards and side effects to be aware of:  Pain, bruising, and bleeding: A small number of patients may have mild, transient bruising, bleeding, or pain where the needle was inserted.  Infection: If the needles are not sterile, there is a risk of infection.  Organ damage: Rarely, an organ may be punctured by a needle that is put inappropriately.  Pacemakers: Light electrical pulses used in acupuncture may cause interference with pacemakers.  Pregnancy: Acupuncture spots that trigger labor may result in an early birth.  Blood thinners: Individuals with bleeding disorders or those using blood thinners may be more likely to hemorrhage.