You can make adult titles searchable if you have a registered account:
IMDB Wrote:Why don't I find adult movies when I perform a search?
The IMDb contains over one million different titles. The aim of the database is to cover as many titles and genres as possible. As a result, some of these titles contain words or expressions that some of our users may find inappropriate and some movies themselves may also fall into this category.
To provide some level of control for those of a sensitive nature some adult titles have been made searchable only by users who are registered with the IMDb and have requested access to this material.
Adult titles cannot be located during a casual search. Only registered users can update their registration profile and activate/deactivate the option to include adult titles in searches and displays.
If you are registered already you can access the adult titles by updating your search preferences and selecting the 'Search Adult Titles/Names' option. Note: The option can only be set from this link.
Here is the page to toggle the adult preference: Search preferences
So if you can enable adult search using the browser should you not be able to enable it with an api too?
I would be extremely grateful if someone can fix a imdb adult scraper!
EDIT I know there are other scrapers for adult movies but imdb has as a lot of older titles which can be hard/impossible to find on other sites.