GCSE requirements for studying medicine at reputable universities usually include five GCSE A* or A's in core subjects, including mathematics and English, usually with three sciences making up the rest. This may include achieving a B grade in a basic science subject such as chemistry, biology, or physics. If you have fewer than 9 GCSE subjects for any reason, perhaps you or your school have dropped out of some subjects, you should contact the medical school for advice before applying. Some like Cardiff will also ask for 66 or BB in Additional Science and Science (what used to be double-prize science) or equivalent.
The broadening of the participation criteria, as well as other access to medicines programs, may allow for a reduction in GCSE entry requirements. Medical schools may insist that you submit to all your GCSE exams within a certain period of time, for example, 12 months. If there are any mitigating circumstances that may have led to a reduction in GCSE's performance, you should ask your referee to include the reasons for this in the reference. If you perform poorly at GCSE, you will need to carefully research medical schools and choose those that have indicated that they pay less attention to their GCSE ratings.
If you truly believe that your reduced performance on the GCSE does not reflect your predicted A-level scores in terms of academic performance, you can request that your referee write something about it in the reference section of the UCAS form. Remember that these are minimum requirements and most successful candidates will have more, usually A and A* (or 7, 8 and 9) in GCSE. This means that medical schools have real evidence of academic performance even before any predicted A-level qualification and therefore excellent performance in GCSE is very important.