What a broad question it is.....just to list some:
1. Increased blood pressure
2. Gynecomastia
3. Water retention and bloating
4. ED
5. Liver stress
6. Head hair loss
7. Increased growth of body and face hair
8. Prostate enlargement
9. Testicular atrophy....
Just to mention some.
However, I have to outline that most of these side effects can be easily prevented or dealt with if you use all the proper ancillaries and run a proper PCT after ending a steroid cycle.