The use of mesembrenone and medicaments and dietary supplements containing mesembrenone. The applicant has surprisingly found that mesembrenone exhibits potent PDE-4 inhibition properties and, in addition to being useful in treating conditions that respond to treatment with a PDE-4 inhibitor, has dual activity on account of its serotonin-uptake inhibition properties. Mesembrenone is extracted and isolated, for example as a pure compound, from plant material of the plant family Mesembryanthemaceae. Preferably a plant or plants from the genus Sceletium, more preferably, Sceletium tortuosum(L) N.E.Br is used.