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.
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 theorized “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.
Several studies have been conducted in recent years to investigate what, if any, role 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 such as longevity and cancer treatment are implausible and unsupported by any research.
More mundane health claims, most commonly pain relief, also lack any credible proposed mechanism, and clinical research is not promising.
Effects of magnet therapy on pain relief beyond non-specific placebo response have not been adequately demonstrated.
A 2008 systematic review of magnet therapy for all indications found no evidence of an effect for pain relief, with the possible exception of osteoarthritis.
It 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.
In 2009 the results of a randomized double-blind placebo-controlled crossover trial on the use of magnetic wrist straps (a leather strap with a magnetic insert) for osteoarthritis were published, addressing a gap in the earlier systematic review.
This trial showed that magnetic wrist straps are ineffective in the management of pain, stiffness and physical function in osteoarthritis. The authors concluded that “reported benefits are most likely attributable to non-specific placebo effects”.