There are a few different options you have for disposing of used needles. If you would like to drop them off at a local sharps disposal site, the website safeneedledisposal.org is a great resource that goes over how to dispose of your sharps safely, and provides a feature to locate local sharps disposal sites near you! You can also drop them off at your local hospital for disposal.
There are also a few different Mail-Back & Container programs you can look into, if you prefer this method! It also looks like Amazon offers a sharps container mail-back service as well.