Much as I love dogs, I'd advise against a puppy, especially a pit bull puppy.
1. They need to be walked at minimum every 4 hours until they're about 8-9 months old. They just don't have the bladder capacity to hold it longer. This could be really difficult if you don't have a stay-at-home partner or no mandatory classes.
2. Pit bulls are wonderful dogs, but it's a b**ch to find a rental that will allow them. Unless you already own a house, you'll likely have a really hard time.
3. Housetraining a dog is REALLY hard. Takes a lot of patience and a LOT of time. Other behavioral training is also pretty time consuming.
If you want a dog, I totally get it. But I'd advise getting an older one from a shelter. Shelters nowadays do a great job of screening dogs, and you'll actually have a better idea of what you're getting into. They'll be able to tell you about its personality and whether it's housetrained.
Puppies are also expensive, and you should absolutely enroll your dog in puppies classes and an obedience class ($200-$250). Proper socialization during a dog's early weeks is important (particularly 10-16 weeks of age), and failure to properly socialize a dog can lead to, among other things, aggression and behavioral problems. These classes can go pretty far in helping with it, and it will make your life easier. Also, with the time constraints of a MS1, think about whether your puppy will get all of the exercise it needs. Puppies are more energetic than older dogs. Don't be fooled if your puppy sleeps a lot at first. My golden retriever puppy was extremely laid back and slept a good portion of the day for the first two weeks, then her energy exploded.
Also factor in the vet bills. The immunizations for puppies are also series, and vaccines aren't cheap (about $250 total, not necessarily counting examination fees, etc.). If you want to potty train your dog, you'll need a crate and a good one that will fit a pit bull will cost approximately $100. And watch your dog like a hawk. My mother threw rib bones in the trash can (despite the fact I had specifically placed the bones where the dog couldn't get to it), and my puppy swallowed a pork rib bone (about 5" whole) on Christmas Eve no less and was forced to take my dog to the emergency vet. Imagine my dismay when I was given three options: Have an emergency endoscopy at $2k-$3k, emergency surgery at $3k, or to wait it out. The point of this anecdote: you should always be prepared for unexpected emergency vet bills. Don't forget that having your dog spayed or neutered can cost $75-$150.
And then comes potential issues with living arrangements. Many landlords will charge non-refundable pet deposits (usually $300-$500+) and/or charge pet "rent" on top of it. This is an additional added cost. And if you have a pit bull, you can be prepared to rule out a number of housing options.
I agree with the other poster that a puppy may not be as good an option for a medical student as a senior dog or at least an adult. They can go longer with bathroom breaks, are less energetic, and with moderate amounts of exercise tend to be much happier. Seniors especially, are often happy with a couple of good walks a day and pretty much want to lay by the heater or on the floor all day. :/
