Qi is considered our vital life force. It flows through channels/meridians in our bodies. Disease inhibits the flow of qi in our bodies. Stress, emotions, physical injury/trauma, constitutional weakness, diet, or the environment can cause this. Acupuncture corrects the imbalances within our bodies by stimulating certain points on the body where the qi comes closest to the surface (acupuncture points). This is done safely and without side effects.
From a western perspective, the stimulation of particular acupuncture points has been shown to induce physiological responses in the body, such as endorphin release, stimulation of the nervous system, and hormone regulation. Labels like acid reflux, fibromyalgia, and luteal phase defect are all Western medical terms. Acupuncture is specific to each individual and is based on that specific person, not the label they have been given for their condition.