As one of the most popular oils used in aromatherapy, grapefruit oil can increase your mental focus and give you a natural pick-me-up. When inhaled, its stimulating effects also make it effective for reducing headaches, sleepiness, brain fog, mental fatigue and even poor moods. Grapefruit oil may even beneficial for healing adrenal fatigue symptoms like low motivation, aches and sluggishness. Some people like to use grapefruit as a mild, natural antidepressant since it can increase alertness while also calming nerves.