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 crystalline modifications, the use of these modifications as well as a process for the enrichment of such crystalline modifications.