I sat my inital Class 1 medical about a month ago and had started a Creatine course about a month or two before that. Didn't have any problems with the medical, but the thing about the creatine is that you take 4-5 teaspoons a day to load up in the first week and then cut back to maintenance portions of 1 per day so I suppose it depends what stage you are at but I am sure it will not cause you any problems.
RR