Indole derivatives of formula I, their salts and solvates, have valuable pharmacological properties together with good tolerability, as they have actions on the central nervous system: wherein R1 and R3 are as defined herein. The compounds have a strong affinity for 5-HT2A receptors, and furthermore exhibit 5HT2A receptor-antagonistic properties. These are therefore suitable both in veterinary and in human medicine for the treatment of functional disorders of the central nervous system and also of inflammation.