Using an 11-item questionnaire and a double-blind experimental design, changes in mood, hunger and food preference after taking caffeine (100 mg), tryptophan (500 mg), tyrosine (500 mg) or placebo, were investigated in 60 volunteers. At the end of the study, volunteers also ranked the four treatments on a sedation/stimulation scale. Caffeine significantly increased scores for wakefulness, vigor, clarity of mind, energy, feeling full of ideas, feeling full of go and feeling efficient. Caffeine was also ranked as the most stimulating treatment (p less than 0.001). Tyrosine produced no changes, while tryptophan shifted mean scores towards somnolent and lethargic, and was ranked most sedating (p less than 0.05). None of the treatments changed hunger ratings or carbohydrate/protein preference.