In this work, we present the first study of highly compressed carbon nanohorns (CNHs). The experiments were performed in a sapphire anvil cell and the morphological changes induced in the CNHs samples were monitored simultaneously by Raman spectroscopy and subsequently by transmission electron microscopy. CNHs samples subjected to a maximum stress of 8 GPa in a single direct compression cycle showed broadened Raman spectra, corresponding to carbonaceous regions with graphite-like structures, surrounded by debundled dahlia-like structures. However, samples subjected to a moderate stress single cycle (2 GPa) exhibited morphological changes from dahlia-like to bud-like structures. Finally, consecutive moderate stress cycles led to the aggregation of such bud spheres towards the formation of a laminar material with horn-like structures at the edges; a very promising configuration for targeted functionalization. This study demonstrates the advantages of using stress for pretreating CNHs samples for subsequent reactivity and functionalization studies.