L-Tyrosine supplies the building block your brain uses to make dopamine and norepinephrine. When you are tired, cold, or under heavy stress, those neurotransmitters deplete faster. Taking tyrosine helps you stay sharp during short term, high pressure demands like an intense work sprint, a long night of studying, or a military operation in harsh conditions. The effect is most noticeable when your cognitive reserves are actually running low.
Take it in the morning or 30 minutes before a mentally tough task. An empty stomach gives you better absorption. Most studies use doses between 500 mg and 2 g.
Skip it if you have hyperthyroidism or bipolar disorder. Do not combine it with MAOIs or levodopa. Those combinations can push your system too far in a dangerous direction.