I don't think people give melatonin as much of a trial as they should. I have heard that some antihistamines such as doxylamine succinate may impair cognition, but I'd like to see the report and if it was widespread. I'd say there are supplements such as sage extract are helpful for memory retention, and melatonin helps too. Sometimes the media exaggerates the effects of some meds. Like Ambien for instance - it is extremely rare for anyone to have the "non-conscious sleepwalking" side effect the media exaggerated. A good-sized Mayo Clinic study explained the condition is rare, and most doctors will not pay attention to the Mayo Clinic report, they stick with their initial misinformative opinions.