I have been on Pramipexole since 2001. I started on a very low dose and increased this over a few months ( note: very, very slowly) until the dose was sufficient to relieve the symptoms it is supposed to treat. By then I had reached the recommended max dose of 4,5 mg a day. I had/have very little problems with bothersome side effects, mainly some foot/ankle oedema for which I wear compression stockings. My main problem was/ is walking, putting one foot in front of the other, not much tremor. What it also did,is improving my mood, I felt better in myself and more confident when out of the house. As the drug was relatively new, more information appeared on medical websites and it mentioned the potential of this drug for helping people with depression. I would not be surprised if that was the case.
Dopamine Agonists mimick the working of real dopamine and in the past (2001) was a favorite first drug for Parky's , but that is no longer the case, it depends on your neurologist what he/she prefers. DAs have a wider range of side effects and therefore are less well tolerated than levodopa drugs, especially the ICD side effect can be devastating for some.
DAs are always very slowly titrated (dose increased),and therefore will take a while before effective dose level is reached.