A composition including as an active ingredient an extract of a plant of the family Mesembryanthemaceae with mesembrenol and mesembrenone as the two major alkaloids present. The invention also relates to the use of the composition as a PDE4 inhibitor and as a serotonin-uptake inhibitor, preferably applied in formulations for the use of the composition as a dual serotonin-uptake inhibitor and PDE4 inhibitor. The invention extends to compositions, such as pharmaceutical compositions or compositions used as dietary supplements, the total alkaloid content of which includes at least 80% (w/w) combined content of mesembrenol and mesembrenone, less than 5% (w/w) mesembrine, and at least 7% (w/w) mesembranol.