Please do not dispose of medication down the sink. Research has shown that traces of medication flushed/drained winds right back up in your drinking water.
In the US, the FDA has listed medications deemed safe to dispose of in the sink than let go in the trash. Worst case scenario, if you cannot find a take-back program, you may throw non-flushable medications in the trash.
http://www.fda.gov/drugs/resourcesf...edicine/safedisposalofmedicines/ucm186187.htm
Many cities in numerous countries also host medical disposal days. I know in Chicago, there is a time in the year where you are allowed to drop all expired medication off at any police station for proper disposal.
Before you dispose of medication in the trash or sink/toilet, please check your local government sites and see if they offer a safer alternative site.