Abstract: Solid and liquid pharmaceutical preparations containing cilansetron or its acid addition salts as active substance which include an amount sufficient to stabilize cilansetron against racemization, of a physiologically compatible water-soluble acid additive selected from monobasic or multibasic organic acids having 2 to 12 carbon atoms with a first p.sub.s value between 1.1 and 4.8, acid salts of the aforementioned multibasic organic acids, and acid salts of multibasic mineral acids having a first available pK.sub.s value between 1.5 and 7.5, as well as the use of such acid additives for stabilizing cilansetron against racemization in pharmaceutical preparations.