adelgazar

v. thin, slim, become thin or thinner

= lose + weight, slim down.
Ex: The article 'Keeping New Year's resolutions while counting down to the new millennium' discusses the following topics: self-discipline; losing weight; stopping smoking; starting an exercise programme; paying off bills; and meeting someone new.
Ex: The abundance of book types and titles makes display and merchandising increasingly difficult; some booksellers are dealing with this by slimming down or cutting out certain categories.
----
* pastilla para adelgazar = diet pill, slimming pill.
* píldora para adelgazar = slimming pill.