If you are truly a medical student, then please don't mislead everyone. Vitamins are not all safe. Vitamin A in particular, in large doses, can be very harmful. It's likely that your dermatologist would not prescribe any amount that is even close to dangerous, but please be careful not to increase your own doseage.
Hypervitaminosis A (an overdose of Vitamin A) can cause a bevy of side effects, including liver damage, eye damage, , birth defects (in pregnant women), and bone density loss. In extreme cases it can cause death.
Like I said, your dermatologist will likely presribe levels WELL within safe margins, but please don't assume that all vitamins are safe.