The present invention relates to crystalline forms of (1r,4r)-6'-fluoro-N,N-dimethyl-4-phenyl-4',9'-dihydro-3'H-spiro[cyclohexane-1,1'-pyrano[3,4,b]indol]-4-amine, pharmaceutical compositions and medicaments comprising these modifications, the use of these modifications as well as to a process for the enrichment of them.