It all depends... are you equating creativity with the productiveness of hypomania (sometimes)? When I think of creativity I think of Kay Redfield Jamison who wrote the book Touched by Fire which has the premise that many truly creative people have bipolar. She has written many books and research articles... perhaps you have heard of her book The Unquiet Mind. Anyway, she takes lithium and remains creative. If you are taking too much then you might have cognitive effects but stopping creativity...no.