There are different types of MS programs.
Some are focused on medical school coursework and are an audition for medical school. These are the "special masters programs" (SMP) that are, essentially, a bet that you can do better in medical school than the average med student. If you win the bet, you have a good chance of being admitted to a medical school; if you lose, you kiss your chances good bye.
There are "record enhancer" MS degrees that don't show you have prowess in the hard sciences but are a way of building a skill-set that may be of value in medical school and beyond. Biostats, biomed engineering, public health would be some examples. Sometimes this is a way to keep loans at bay and show that you are doing something productive during the year you apply to medical school. In some cases, it is an alternative to finding a job in a tight job market.
There are MS degrees that are neither record enhancers nor SMP.