If you see zero volume for monthly searches for your keyword research with AnswerThePublic, please note that any adult or sensitive keywords are automatically filtered out and removed. You won’t be able to perform any searches that have that kind of content.
We've seen similar issues with other keywords that fall into any of the following categories:
1. Highly regulated medical & financial topics
2. Drugs/Psychoactive products
3. Controversial health topics
4. Guns and weapons
5. Children-related content
They are also under Google’s advertising policies on prohibited content.
In those cases, you will end up having to use other tools to find more information for those keywords.