Table 2.

Summary of the preclinical and clinical data pertaining to the CNS activity of EOs.

Plant/Source	Essential Oil	Test Subjects/Animal Model	Route of Administration Tested	Effective Dose/Preparation Technique	Experimental Outcome	Purpose of Use	References
Syzygium aromaticum	Clove oil	90 BALB/male mice (27–32 g)	Intraperitoneal injection	50,100, and 200 mg/kg of aqueous/ethanolic extract of clove in a final volume of 10 mL/kg	Maximal percent effect (MPE) of animals that were tested on hot plate and treated with oil was higher than that of the control group	Analgesic	[4]
Boswellia sacra, Boswellia frereana	Frankincense oil	Adult male Sprague Dawley sleep-deprived rats	Topical application	50 μL in a 1:1000 dilution with jojoba oil on the nape of neck for 5 h with hourly intervals	Corticosterone and glutathione levels declined, wakefulness time increased, and non-rapid eye movement time declined	Antidepressant, mood elevation, anxiolytic, and stress relief	[8]
Lavandula angustifolia	Lavender oil	200 pregnant women undergoing cesarean section	Olfactory administration	2 drops (1% cc) of 2% lavender essence applied with a cotton swab to oxygen face mask, which was used for 3 min, repeated thrice over different time periods	Mean Visual Analogue Scale (VAS) decreased significantly, indicating amelioration of pain	Analgesic	[63]
Cymbopogon citratus	Lemongrass oil	30-day old adult swiss male mice	Oral administration	Doses of 1, 5, and 10 mg/kg provided as well as repeated dosing for 14 days	Anxiolytic effects observed through results obtained in light/dark box test	Anxiolytic	[20]
Cananga odorata	Ylang ylang oil	29 male participants	Olfactory administration	Participants placed in a closed room for 60 min that was previously fragranced with ylang ylang oil for 20 min.	Decline in systolic and diastolic BP and reduction in heart rate	Sedative effect and mood adjustment	[25]
		Male and female mice weighing 25–30 g and 22–25 g, respectively	Olfactory administration	Stainless steel square inhalation apparatus (65 × 65 × 45 cm) with controllable heater to heat oil/water emulsion containing ylang ylang oil (1% v/v) and benzyl benzoate (2% v/v). Mice placed in chamber for 10 min	Male mice experienced more changes in concentration of neurotransmitters than female mice. Decline in DA in striatum and 5-HT concentration in hippocampus and decreased ratio of 5-HIAA/5-HT	Anxiolytic effect on male mice	[24]
Cinnamomum verum	Cinnamon oil	Male albino mice	Intraperitoneal injection	0.5–2 mg/kg body weight three times a day or once daily for 14 days	Decreased immobility time in forced swim test (FST) and tail suspension test (TST) Mice treated with 2 mg/kg spent a longer time and showed more entries into the open arms of elevated plus-maze (EPM)	Antidepressant and anxiolytic	[29]
Eucalyptus globulus	Eucalyptus oil	28 individuals with osteoarthritis that underwent total knee replacement surgery	Olfactory administration	3% v/v was dissolved in almond oil, placed on 4 × 2 gauze pad, and inhaled for 30 min for 3 consecutive days	VAS scores after aromatherapy decreased. Heart rate increased to 0.3+/− 0.6 beats/min on day 1 and decreased to 1.7+/−1.7 beats/min and 0.6+/−1.0 beats/min on days 2 and 3, respectively	Analgesic, lowering BP, stress relief, and anxiolytic	[38]
Mentha piperita	Peppermint oil	144 healthy individuals 24 participants (9 male/15 female) (mean age 25.2 years)	Olfactory administration Oral administration	4 drops of oil in a diffuser pad followed by 5 min of inhalation 2500 µL capsules containing 50–100 µL of peppermint oil in vegetable oil	Enhanced alertness and memory 100 µL dose caused an improvement in rapid visual information processing task (RVIP) performance at 1 h and 3 h post-dose. Both doses decreased fatigue	Memory booster, modulated performance on cognitive tasks, and decreased mental fatigue	[42,45]
	Rosemary oil	20 healthy individuals	Olfactory administration	Inhalation of 10% v/v of the oil for 20 min using an oxygen pump attached to a respiratory mask whose airflow rate is 2 L/min	Decreased both powers of alpha1 and alpha2 waves	CNS stimulant	[64]
Rosmarinus officinalis		140 healthy individuals	Olfactory administration	4 drops of oil in a diffuser pad followed by 5 min of inhalation	Mood elevation increased blood pressure, heart rate Improved mood and enhanced quality of memory	Memory enhancer	[62]
Salvia sclarea	Sage oil	45 healthy individuals 135 healthy individuals	Olfactory administration Olfactory administration	5 drops of EO in 5 mL of water along with an aroma stone 5 drops of EO in 5 mL of water along with an aroma stone	Memory enhancement Improved and enhanced memory and secondary memory	Memory enhancement Memory enhancement	[52,65]
Santalum paniculatum	Sandalwood oil	D-galactose mediate oxidative stress-induced Swiss male albino mice (20–30 g)	Intraperitoneal administration	1 g/kg body weight of sandalwood oil in 5% Tween 80 in saline for a week	Oxidative stress status ameliorated in group-administered sandalwood oil. Recovery of GSH, NO levels, catalase, and lipid peroxidation status in liver. Reduction in serum bilirubin, SGOT and SGPT.	Antioxidant	[59]