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Magnet therapy, magnetic therapy, or magnotherapy is a pseudoscientific alternative medicine practice involving the use of weak static magnetic fields, a form of electromagnetic radiation, produced by permanent magnets. It is similar to the alternative medicine practice of electromagnetic therapy, which uses the same sort of EM radiation, but generated from electrically powered devices.
Practitioners claim that subjecting certain parts of the body to weak EM fields has beneficial health effects. These physical and biological claims are unproven and no effects on health or healing have been established. Although hemoglobin, the blood protein that carries oxygen, is weakly diamagnetic (when oxygenated) or paramagnetic (when deoxygenated) the magnets used in magnetic therapy are many orders of magnitude too weak to have any measurable effect on blood flow. This is not to be confused with trans-cranial magnetic stimulation, a scientifically valid form of therapy 
Methods of application
Magnet therapy is the application of the weak magnetic field of permanent static magnets to the body for purported health benefits. Different effects are assigned to different orientations of the magnet.
Products include magnetic bracelets and jewelry; magnetic straps for wrists, ankles, knees, and back; shoe insoles; mattresses; magnetic blankets (blankets with magnets woven into the material); magnetic creams; magnetic supplements; plasters/patches and water that has been "magnetized". Application is usually performed by the patient.
Suggested mechanisms of action
Perhaps the most common suggested mechanism is that magnets might improve blood flow in underlying tissues. The field surrounding magnet therapy devices is far too weak and falls off with distance far too quickly to appreciably affect hemoglobin, other blood components, muscle tissue, bones, blood vessels, or organs. A 1991 study on humans of static field strengths up to 1 T found no effect on local blood flow. Tissue oxygenation is similarly unaffected. Some practitioners claim that the magnets can restore the body's hypothetical "electromagnetic energy balance", but no such balance is medically recognized. Even in the magnetic fields used in magnetic resonance imaging, which are many times stronger, none of the claimed effects are observed. If the body were meaningfully affected by the weak magnets used in magnet therapy, MRI would be impractical.
Several studies have been conducted in recent years to investigate what role, if any, static magnetic fields may play in health and healing. Unbiased studies of magnetic therapy are problematic, since magnetisation can be easily detected, for instance, by the attraction forces on ferrous (iron-containing) objects; because of this, effective blinding of studies (where neither patients nor assessors know who is receiving treatment versus placebo) is difficult. Incomplete or insufficient blinding tends to exaggerate treatment effects, particularly where any such effects are small. Health claims regarding longevity and cancer treatment are implausible and unsupported by any research. More mundane health claims, most commonly about anecdotal pain relief, also lack any credible proposed mechanism and clinical research is not promising.
The American Cancer Society states that "available scientific evidence does not support these claims". According to the National Center for Complementary and Integrative Health, studies of magnetic jewelry haven't shown demonstrable effects on pain, nerve function, cell growth or blood flow.
A 2008 systematic review of magnet therapy for all indications found insufficient evidence to determine whether magnet therapy is effective for pain relief, as did a 2012 review focused on osteoarthritis. Both reviews reported that small sample sizes, inadequate randomization, and difficulty with allocation concealment all tend to bias studies positively and limit the strength of any conclusions.
These devices are generally considered safe in themselves, though there can be significant financial and opportunity costs to magnet therapy, especially when treatment or diagnosis are avoided or delayed.
A 2002 U.S. National Science Foundation report on public attitudes and understanding of science noted that magnet therapy is "not at all scientific." A number of vendors make unsupported claims about magnet therapy by using pseudoscientific and new-age language. Such claims are unsupported by the results of scientific and clinical studies.
Marketing of any therapy as effective treatment for any condition is heavily restricted by law in many jurisdictions unless all such claims are scientifically validated. In the United States, for example, U.S. Food and Drug Administration regulations prohibit marketing any magnet therapy product using medical claims, as such claims are unfounded.
- Russell, Jill; Rovere, Amy, eds. (2009). "Magnetic therapy". American Cancer Society Complete Guide to Complementary & Alternative Cancer Therapies (2nd ed.). Atlanta, Ga.: American Cancer Society. ISBN 978-0944235713. See archived online version "Magnetic Therapy". 1 November 2008. Archived from the original on 12 November 2012. Electromagnetic therapy is a related field. See chapter in ACS book just referenced, and archived ACS webpage on that.
- Park, Robert L. (2000). Voodoo Science: The Road from Foolishness to Fraud. New York, New York: Oxford University Press. pp. 58–63. ISBN 0-19-513515-6.
Not only are magnetic fields of no value in healing, you might characterize these as "homeopathic" magnetic fields.
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- Magnetic Therapy: Can magnets alleviate pain? by Cecil Adams — The Straight Dope
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- Magnet therapy in the Skeptic's Dictionary by Robert Todd Carroll
- Magnet therapy — editorial in the British Medical Journal
- Magnet Therapy: A Skeptical View by Stephen Barrett — Quackwatch