I was set on doing a PhD for a year or two as an undergrad. I was working as a research assistant, I was planning to do a summer research internship, and I was going to travel to South America to do some research. I was quite the biology nerd and I ate the stuff up.
But I eventually changed my mind. I found that physiology, pharmacology, and disease were far more interesting to me than classifying transmembrane receptor protein subunit types in rat brain or mapping phenotypic traits to QTL in llamas (two projects I worked on). Research takes a long time, has little immediate clear impact on anything, is often frustrating and difficult, and rather tedious. One of the projects I was working on lost funding. Years of work had to be pretty much scrapped. My PI was left writing yet another grant proposal to work on something completely different.
I knew I liked to teach, so I thought maybe a PhD was a good route for that reason too. But I saw that there wasn't a lot of autonomy in teaching at a university. As a new professor you got stuck with the crappy 100 level class with whiny freshman. Or you had to use a textbook the department liked but you don't. Or you have to teach a subject you don't know anything about but they need someone to fill in.
I wanted to be able to work with people and see results sooner than 3 years later. I wanted to be able to be involved in research if I wanted, but from the clinical side. I wanted to be able to teach, but may just as an attending to residents and interns.
I did consider doing a PhD and even MD/PhD very, very seriously. In the end I decided I liked the pros and cons of medicine more than the pros and cons of academia. Both have great things going for them, both have big downsides. I chose what looked best to me.
