L-Tyrosine is an amino acid found in the diet that is metabolized to produce catecholamines such as dopamine and adrenaline. It is also used in the production of thyroid hormones. For these reasons, weight loss and preworkout supplements often include it.
When it comes to the topic of actually increasing dopamine and adrenaline outright, L-tyrosine does not seem to hold much promise. The synthesis of catecholamines is highly regulated in the body, so simply increasing the amount of L-tyrosine in your body does not necessarily increase catecholamine production.
However, some studies have noted that in stressful situations where noradrenaline exerts a protective effect, supplying L-tyrosine seems to provide a 'safety buffer' of building blocks that can prolong the anti-stress effect of catecholamines by delaying their depletion. This has been noted in situations of cold stress, psychological stress, and sleep deprivation in humans but at a relatively high dose of 150mg/kg. Improvements in memory and attention during stressful situations have been found, though the effect doesn't appear to be very big or reliable.
It's generally safe. It's one of the basic amino acid that makes up proteins in the human body, so while that doesn't mean that any amount is safe, it does suggest that the body knows how to handle it safely.