Same thing - both are customization of healthcare, with medical decisions, treatments, practices, or products being tailored to the individual patient

Both terms have been often used interchangeably. But based upon few historical reports, precision medicine is the new terminology. Literally meaning creating drugs or device for individual patient.

The term personalized medicine was susceptible to misinterpretation and therefore U.S. National Research Council in 2011 made suggestion for the term precision medicine.

Below are few article debating the same concept which are interesting to read: -

National Research Council. 2011. Toward Precision Medicine: Building a Knowledge Network for Biomedical Research and a New Taxonomy of Disease. ISBN: 978-0-309-22222-8

An, Gary and Vodovotz, Yoram. 9 March 2015. What Is “Precision Medicine” — And Can It Work? Elsevier Connect; 

Plenge, Robert M. 16 March 2013. Personalized Medicine vs. Precision Medicine. Plenge Gen Blog

Both These terms are used interchangeably

As Dr. Rimple said its true they are interchangable. Main aim behind this is Tailoring the Drug therapy to get maximum health benefits with minimum or no adverse events thus reducing cost of treatment and improving the quality of life.

Focusing mostly on drug therapy misses the point of treating every patient as a specific case. Regular medicine's "one size fits all", produces a "knee- jerk reaction" where every 'symptom' gets the same Rx. Giving an analgesic for a headache misses the point completely. Personalized medicine would endeavor to find the cause of the cause, expressed as a 'headache'. This is why no new patient is encouraged to say anything, until I have finished my diagnoses. Then, reporting what I found, most of the time their 'complaint' has already been answered.

Thanks Dr Carlos for valuable input