The problem is
foreach (string itemchecked in DrugsList.CheckedItems)
What you need is
foreach (object itemchecked in DrugsList.CheckedItems)
{
DataRowView drv = itemChecked as DataRowView;
cmd.Parameters.Clear();
cmd.Parameters.AddWithValue("@DrugsValue", drv["DisplayMember or ValueMember"]);
cmd.ExecuteNonQuery();