Physician: The hormone melatonin has shown promise as a medication for sleep disorders when taken in synthesized form. Because the long-term side effects of synthetic melatonin are unknown, however, I cannot recommend its use at this time. Patient: Your position is inconsistent with your usual practice. You prescribe many medications that you know have serious side effects, so concern about side effects cannot be the real reason you will not prescribe melatonin.

The patient's argument is flawed because it fails to consider that

• Athe side effects of synthetic melatonin might be different from those of naturally produced melatonin  
• Bit is possible that the physician does not believe that melatonin has been conclusively shown to be effective  
• Csleep disorders, if left untreated, might lead to serious medical complications  
• Dthe side effects of a medication can take some time to manifest themselves  
• Eknown risks can be weighed against known benefi ts, but unknown risks cannot