This page of the Returnal guide explains the importance of adrenaline in the context of fighting monsters. We explain how to increase adrenaline and under what circumstances the accumulated adrenaline can be lost.
Adrenaline in Returnal is a temporary stat bonus, which is awarded for a flawless playthrough.
Information about the current adrenaline status is displayed at the bottom of the screen. Its initial value is 0. We can increase our adrenaline levels with every 3 enemies we kill. We can't charge adrenaline in this way without any restrictions. The maximum adrenaline level is 5 and it will not be further increased once you reach it.
Advancing to the next adrenaline levels provides you with random rewards - effects. For example, we may be rewarded with improved overload, extending the possible supply of Obolite or vision buff. Information about the type of unlocked effect is displayed along with information about advancing to the next adrenaline level.
When you developer your adrenaline up to level 5 for the first time, you'll unlock the Adrenaline Spike trophy.
Note that adrenaline level can be increased with consumables (Apex Sphere from the image above). This way, we can ensure random effects without having to attack enemies.
Receiving any injuries (e.g. from the attack of the enemy or springing a trap) leads to a reset of adrenaline. We will have to develop it from scratch and we will unlock different effects. If you have gained useful stat bonuses, it is worth playing a little more carefully in order to keep them active for as long as possible.