Small pale yellow circle pill no marking?

Any prescription or over the counter drugs in the US must have some kind of identifying markers on them-letters, numbers, logos or in combination. Supplements, vitamins and herbs do not fall under this law though so many times when you find a plain unmarked pill, it is a supplement of some kind (vitamin, mineral, herbal etc) The other possibilities are illegally made drugs or drugs from another country. There is no way to find out what an unmarked pill is without subjecting it to a laboratory chemical analysis (which would be very expensive), not even a pharmacist would be able to identify them with certainty. You are best off disposing of them.