problem with distinct not distincting...

I have a pretty basic query;

select distinct on (name) name, length(name) from
drugs
where customer_id IS NOT NULL
order by name;

which I'd expect to only return me a single drug name if there are
duplicates, yet I get

name | length
==========
Roaccutane | 10
Roaccutane | 10

table encoding is UTF8...

I'm scratching my head!

Thanks,

John.