There was a slight API change when v0.10.0 was released. Try this:
var drugSource = new Bloodhound({
datumTokenizer: function(d) { return Bloodhound.tokenizers.whitespace(d.num); },
queryTokenizer: Bloodhound.tokenizers.whitespace,
remote: '/drugs/autocomplete?query=%QUERY'
});
drugSource.initialize();
$('#drug_search').typeahead(null, {
name: 'drug',
source: drugSource.ttAdapter()
});
For more details about what changed with the v0.10.0 release, you can refer to the migration guide.