I had been buying them from the vet, for around $30-40 a month. Some meds for dogs are the same as for people, just in smaller doses, I guess. So, I got on the phone and started calling pharmacies to compare prices. I found one that carried the 3 types I needed for $4 a month each. They said they would even deliver, if I ever needed it. Gas, another savings!
For more information: www.ehow.com/how_2051972_donate_prescription_drugs/
A nurse once told me to boil them in water, then dump them in kitty litter before throwing them away. I'm not sure how effective this method is, so check with a professional first.