Four A Levels

I am just starting my A Level's and have chosen Maths, Biology, Chemistry and History however I am debating dropping history as the work load is so big i am worried that it will effect my other subjects and i want to know whether...

-having 4 subjects gives me any advantage than medical applicants with 3?
-it is a contrasting subject so would that make me stand out in the application process at all?
-what must i get in my fourth subject if i was to take it?

When you say you've started your A-levels, does this mean you're in year 12 or year 13? If the latter, then no, for most medical schools four A-levels won't give you any advantage over people with three A-levels except at Bart's and the London because they use UCAS points so the more A-levels you have, the better your chance of getting interviewed/made an offer.

If the former, then the rules are likely to change for you due to A-level reform. In the old system, most medical schools would demand three full A-levels and four AS subjects with a specific grade in the fourth AS subject that isn't taken to full A-level e.g. UCL's standard offer is A*AAe (meaning you need at least an E in a fourth AS if not taken to A2), QUB's standard offer is AAAa etc.

so would just 3 full a levels not be enough?

I am just starting my A Level's and have chosen Maths, Biology, Chemistry and History however I am debating dropping history as the work load is so big i am worried that it will effect my other subjects and i want to know whether...

-having 4 subjects gives me any advantage than medical applicants with 3?
-it is a contrasting subject so would that make me stand out in the application process at all?
-what must i get in my fourth subject if i was to take it?

so would just 3 full a levels not be enough?

In the new system, it is likely that offers will still be based on 3 full A-levels but since there are significant reforms to A-levels being rolled out across England and Wales, there is no way to tell what university policy is going to be as there is still one more application cycle to go through which people with the old A-levels will pass.

I suggest you keep an eye on www.ucas.com for statements made by universities as they'll probably announce what they're going to do to accommodate these reforms. Until the ones that you want to apply to release their decisions, it's not a wise move to drop the fourth subject. It's really stupid of the universities to take their time with this to be honest, since people need to decide now whether they're taking the full A-level or not...