One item re: polypharmacy I haven't seen discussed is the effect of certain drugs (example, for hypertension) on concurrent lifelong rare neurological conditions which get grossly exacerbated by a common drugs. In my own case prednisone caused delirium, as did a CNS stimulant. If the offending drug has a long half-life, one is virtually disabled by that drug till it wears off. Most CNS drugs, be they anxiolytics, stimulants, SSRI type antidepressants cause horrible effects, including gait disturbance (staggering). The clinical trial with thalidomide for another conditon even at low doses left me a profoundly sleepy, forgetful, bedwetting (nightly), delirius, staggering vegetable that was unable to think well enough to get off the trial. The prescribing physician often does not understand my symptoms because they've not heard of them in relation to their prescribed medicine. I'm now on hypertension medicine which has disasterous neurological side effects. The physician does not understand because I'm unlike his other patients. So it's a struggle for which I've launched another lengthy search for another physician, and I suppose after a few years I might find a doctor who listens or measures or refers to measure objectively the side effects.
Not all drugs cause such side effects, and if they have a short half-life, they can be taken prior to bedtime. That has been my experience, but it takes a long time to find a suitable prescribing doctor.