Perhaps the trickiest misconception about quackery is that personal experience is the best way to tell whether something works. When someone feels better after having used a product or procedure, it is natural to give credit to whatever was done. However, this is unwise. Most ailments are self-limiting, and even incurable conditions can have sufficient day-to-day variation to enable bogus methods to gain large followings. In addition, taking action often produces temporary relief of symptoms (a placebo effect). For these reasons, scientific experimentation is almost always necessary to establish whether health methods are really effective. Instead of testing their products, multilevel companies urge customers to try them and credit them if they feel better. Some products are popular because they contain caffeine, ephedrine (a stimulant), valerian (a tranquilizer), or other substances that produce mood-altering effects.
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