<p>Dynamic analysis of structures is one of the most essential techniques for designing earthquake-resistant structures in high-seismicity areas such as the Tehran metropolis. The selection of the acceleration time history of previous earthquakes for utilization in the dynamic analysis is challenging while the chosen ground motions must be not only proportionate to the seismic capacity of the region but also matched a target response/design spectrum. The uniform hazard spectrum (UHS), derived from probabilistic seismic hazard analysis (PSHA), comprises large spectral values at all periods and is too conservative when used as a target for scaling ground motions. An alternative approach is to use the conditional mean spectrum (CMS), which provides a response spectrum conditioned on a spectral acceleration value associated with a unique target period. This alternative procedure is introduced as an appropriate method for selecting and scaling proper ground motions to be used as input for structural dynamic analysis. This study develops the conditional mean spectrum for selected sites in the Tehran region. To this end, a comprehensive PSHA was conducted for the metropolis of Tehran. Subsequently, employing the UHS obtained from the PSHA and the results of the subsequent deaggregation process, the CMS was generated for different sites in the region. The distinction between the CMS and the UHS significantly influences the dynamic behavior of various structural systems in the region. For short-period structures, such as low-rise buildings, the CMS effectively mitigates the unrealistically high spectral accelerations predicted by the UHS at longer periods, resulting in a more rational distribution of seismic demands. In contrast, for long-period structures, including high-rise buildings, the CMS alleviates the overly conservative short-period spectral accelerations associated with the UHS. This results in more realistic force–deformation demands and an improved representation of expected structural responses. Consequently, the application of the CMS directly impacts seismic design decisions and material requirements. The results indicate that CMS-based design can reduce unnecessary conservatism and associated construction costs, particularly for structures sensitive to long-period demands. Furthermore, the findings suggest that the design spectra of the Iranian Seismic Code should be re-evaluated, especially for near-fault sites, to better reflect period-dependent seismic hazard characteristics.</p>