Compositions comprising L-tryptophan, 5-hydroxytryptophan and/or D-Limonene are used for preparing a product suitable for sublingual or nasal administration which is helpful in suppressing appetite in such a manner as to promote weight loss in an individual; such compositions furthermore exhibit an antidepressant activity and an antiasthenic effect which makes them helpful in improving tone and mood and the level of attention in an individual. The compositions preferably comprise phenylethylamine in a synergistic combination which substance is contained in an algal plant extract, preferably of Klamath algae.