1. 1st semester:
you will find it is hard because of especially biology, chemistry, biophysics etc. for example there are many students who need to re-take chemistry mid-terms due to their bad results of first trials of midterms. But it is just a begining of your hard time; meaning the first semester is the easiest time.
2. 2nd semester:
From the 2nd semester, it will be harder because of anatomy and histology. Furthermore you are going to face final exams such as biology final and biophysics final in its exam period; these include the contents of 1st semester needless to say the content of 2nd semester. In case of biology, you are going to have 150 topics. You will see how hard it is.
3. 3rd semester:
I don't know it will be harder than 2nd semester. But upper year students say it gets even harder. we are going to have physiology(9 credit subject), immunology. Although we don't have biology and biophysics anymore.
4. 4th semester:
This exam peiord is a key point, I have heard, it is because we have anatomy final and biochemistry final (+physiology final). Don't forget biochemistry. It is a medical school thus everybody knows we need to learn anatomy, and that is how students focus too much on it, and don't have much time left for other subjects and that is how they fail biochemistry; I have heard that 60% of people fail it.

These are the first 2 years and are called basic module. The 3rd year is now named pre-clinical module and from 4th year on are called clinical module, people say which become much easier and no one fail any more.