Selecting rows by content of array type field

I have table like this:
CREATE TABLE messages {
recepients varchar[],
};

Want to select by content co array type field recepients:
SELECT * FROM messages where 'john' ANY (recepients);

If i want to create index on recepients field, is it enough to

CREATE INDEX messages_recepients_index ON messages (recepients);

or is there other way how to index this? Expressions?

Thanks