Dosage: 500mg. -- 2000mg.
Duration: 2hr. -- 6hr.
Phenylalanine is the direct precursor of tyrosine. Much the same effect is gained from taking d,l-phenylalanine, however, for many it seems the effects are stronger and more positive with l-tyrosine - less product is thus needed.
A few caps in the morning (500mg. -- 1000mg.) is a good maintenence level dose, especially if you are not a coffee consumer - or drink de-caffeinated coffee. This dose gets your brain churning, usually without any sort of speedy effects. However, when taken daily, a tolerance will be noted - best to take sporadically, or every other day or such.
Same dose can be effective in helping to keep your mind awake when you need to pull an all-nighter, be it to party harder or get some work or studying done.
Hangover cure!!! Take 1500mg. (usually 3 caps) the "morning after". Also a good idea to take your favorite headache cure (mine being Naproxen sodium - Aleve©). When taken upon waking up and feeling like the neighborhood dog's ass - you will gain relief in 30-60 minutes. This works! But don't rely on it too heavily.
Doses of 1500mg. + either heal you energetically (as above), or boost your energy sygnificantly. Ideal for sports, working out, etc...without that pesky jittery feeling.
These products are most effectively utilized when taken on an empty stomach mixed with juice or water.
Adequate cofactors (vitamins B6 and C) should also be taken if not included with the product.
Hope that helps