First of all, there is no definite limit to the number of authors who publish medical papers. Generally, 3-4 authors are common, including the first author and correspondent author, as well as the second and third authors. This is because some papers can't be completed by one person, and need the cooperation and research of the group. But some papers have seven or eight authors, and the number is not as large as possible. Generally, the first author and the correspondent author are recognized. We often see some requirements for professional title evaluation. The author must be the first author of the published paper, but this is not the only requirement, and some regions and units do not need it.
Secondly, the maximum number of authors in a paper is related to the length and workload of the paper. Some papers involve a huge workload, which requires experiments, surveys, data collection and even the cooperation of a team. There are as many as a dozen authors in a paper. For the general unit, there is no clear requirement for the evaluation of the author's title, as long as there is a paper published. However, some units, such as scientific research units and universities, are required to publish papers as the first author. It also needs to follow the regulations of local personnel departments, as long as it does not violate national policies.
What do you mean by first author and correspondent?