It really depends on how well you get on with it. For some people, 4 A-levels is too much, but for others, they can manage it.
Do you enjoy the subjects?
Are you good at the subjects?
Are you orgnanised?
Also, think about if you actually need all 4 for your desired course as universities will only consider 3 grades. I haven't done any research into Medicene/Dentistry as it's not my choice of course, but do you need Physics for it? if you were to drop any, to me, Physics seems like the better one to drop.