A. Wallace’s Answer
Well it really depends on what you want to do in the future. The reason to go into a MD Ph.D program is because people have a passion to do research as well as to care for patients clinically. Some individuals do research from a clinical perspective, and other md/ph.ds do research in the wet laboratory, that is in basic biomedical sciences.
Adding the PHD on to the MD will take an additional 2 years or so of graduate school, and perhaps more depending on what your ultimate goal is. That's in addition to the four years of medical school and internship and residency that follows this. So it's really important to be passionate about the research side before deciding to pursue a career like this as its a long time before you are out of training.
Having said that, the md/ph.ds in medicine generally are the individuals who lead the Cutting Edge of medical Sciences, and it has always been my experience that they find particular satisfaction in working in the laboratory to try and cure the diseases they see in the clinic. Typically they end up working in large academic institutions, such as in medical schools. So if that's the kind of thing you are interested in, and if you really like the research side of medicine, considering an MD Ph.D program would certainly be appropriate.
On a personal note, although I am now retired, I spent much of my career doing exactly this, working both in the lab and clinic. I wouldn't have had it any other way!
Best of luck in your search!