Return to pharmacy. Whether or not there are small kids around, unused prescription medicines should be returned to the pharmacy to be incinerated. Dumping them into the sink or toilet ends up putting more of those chemicals into our water supply, not a good idea.
A drug drop-off site. A city may have medicine drop-off sites, such as at some pharmacies. If no drop-off site is available, consider throwing the medicine (in its container) into the regular trash. Hopefully, the medicine will stay in its container in the local landfill for hundreds of years. If a medication is dumped outdoors or flushed down the toilet, it may end up in our lakes, streams, drinking water, and fish.
Except for rare meds. ...That are highly hazardous for whatever reason, flushing the pills and liquids down the toilet and then disposing of the empties normally seems best.
Remove them safely. It is best not to flush them or pour them down the trash due to concerns about contamination of water supply. Due to limitations in space, i will refer you to a good website for further details: http://www.Jbmhh.Army.Mil/sites/local/inc/pharmdisp.Pdf. Many items can be safely disposed in household trash. Read the link for more details.