L-tyrosine

Probably only in narrow situations. A 2015 review found oral tyrosine can help cognitive performance in short, stressful or demanding situations, with minimal benefit for exercise and limited promise for clinical disorders. A small trial saw a gain on a hard memory task, not an easy one. We found no strong evidence it sharpens focus in rested people.

There's no official dose. Bottles usually list 500 mg to 2 g per serving. The trials that found a short-term cognitive effect mostly gave one dose of 100 to 150 mg/kg, roughly 7 to 10.5 g for a 70 kg adult, about an hour before a demanding task. One field trial used 2 g daily for 5 days. No trial compared doses head to head.

Not on current evidence. A 1989 study infusing N-acetyl-L-tyrosine into the bloodstream found most of it left in urine unchanged, and a 1994 piglet study found 65% excreted unchanged. Neither tested an oral supplement, but nothing we found shows NALT's better solubility improves tyrosine delivery. Most cognitive research used plain L-tyrosine.

In the trials we reviewed, it was mostly well tolerated. The notable finding was a modest blood pressure dip: a brief diastolic drop after one dose, and lower systolic pressure over 5 days of daily use. A 4-week trial in 65 people found no tyrosine-specific side effect against placebo. Nothing runs longer than that. A liver failure case report involved a multi-ingredient product containing NALT, and tyrosine could not be singled out.

Ask a doctor first. No trial tested tyrosine alongside specific drugs, but it's the precursor of dopamine, norepinephrine and thyroid hormone, so stimulant medications, antidepressants, levodopa, thyroid medication and MAOIs are the ones to flag. Tyramine, not tyrosine, causes the MAOI blood pressure spike, but the two share an enzyme pathway, so interaction resources advise caution.