Q: Can I cite a paper that has been accepted but not yet published?

You can cite any paper that you want: a published paper, a pre-print, a submitted paper, or a paper that has been accepted but not yet published.  Some journals may not encourage citation of pre-prints, but there is no such issue with papers that have been accepted for publication. Since these papers have been peer-reviewed, they are considered just as reliable as published papers. Generally, for such papers, you need to use the term “in press” after the title in the reference list.

However, if your paper relies heavily on an unpublished paper, it is better to provide a copy of that paper or include it in the supporting online material that you provide. Alternatively, the paper can be archived in an appropriate database and made available to reviewers.