I did 2 blood test this year.
One in februaray and one in June. Both came with the exact dopamine level 11ng/dl (10-110). Is that not curious?
I also feeling the less dopamine: Less motivation in general, less focus, less happines (but curiously my serotonin levels were ok and I feel in a relaxed and calm state most of the time).
Also I took L-tyrosine 1g to 2g / day for a week and I entered into a state of real focus and motivation for 4 days. The most focus that I had in a long long long (maybe never) time. I remember especially 2 days that I worked in my career project since the morning to the 1AM, only have rested for lunch and dinner for a maximun of 40min. Obviously after that I think I got a drawback and I could have had a brief psycotic-attack caused by it, in the form of paranoias and little hallucinations. Yes its documments that dopamine agonist could induce it (fortunatly).
Having not taking it since then and now started to recover motivation and focus, but nowdays Im not eating any sugars that drive my energy very low, and I try to avoid carbs unless is the morning that somedays I take some toast with butter. Maybe I should give another try with the L-tyrosine I dont know yet.