Exploration of the validity of weak magnets as a suitable placebo in trials of magnetic therapy

SummaryObjectiveTo investigate whether 50 mT magnetic bracelets would be suitable as a placebo control condition for studying the pain relieving effects of higher strength magnetic bracelets in arthritis.DesignRandomised controlled comparison between groups given either a weak 50 mT or a higher strength 180 mT magnetic bracelets to test.SettingFour arthritis support groups in Devon, UK.ParticipantsOne hundred sixteen people with osteoarthritis and rheumatoid arthritis.Main outcome measureBeliefs about group allocation and expectation of benefit.ResultsThere was no significant difference between groups in beliefs about allocation to the ‘active magnet’ group. Participants were however more likely to have an expectation of benefit (pain relief) with the higher strength magnetic bracelets.ConclusionsAsking about perceived group allocation is not sufficient to rule out placebo effects in trials of magnetic bracelets which use weak magnets as a control condition. There are differences in expectation of benefit between different magnet strengths.