Short answer: Check what your teachers and exams use. For many stable topics, one edition back is workable, but guidelines and clinical content change.
What changes between editions
Basic sciences change slowly, while clinical guidelines, drug information and imaging update more often.
How to decide
Ask a senior or faculty member which edition they use, and compare the contents of the older and newer edition if you can.
Cost versus risk
An earlier edition costs less but may miss recent updates. Weigh the saving against the subject: clinical subjects are riskier than basic ones.
Related: sell medical books.
Frequently asked questions
Can I use an older edition?
Often yes for stable basic subjects. Check with your faculty for clinical subjects.
Where can I sell old medical books?
You can list them on Bookaao and receive the sale amount after delivery, minus the platform fee.