Not all doctors will automatically give you the exact equivalent of what you were taking in the US.They will prescribe what they think is right for you, based on their knowledge and experience, which may differ from what your US doctor thought.
For example, I used to take Singulair for allergic asthma. Although they have Singulair in the UK, I was told that doctors usually only prescribe corticosteroids for asthma. So since my asthma isn't bad enough to warrant the side effects of corticosteroids, and since I really only took Singulair because I used to have cats which I'm allergic to, and I don't have cats anymore, I just don't take asthma meds. Though I carry around an emergency inhaler just in case.
Also, I was on a triphasic birth control pill in the US and put on a monophasic one in the UK.