We present results obtained with the updated version of our code medea2, which includes all physical processes necessary to study the energy deposition in the surrounding environment from primary photons and fast leptons produced by dark matter (DM) particle decay/annihilation. Such interactions now include also Compton scattering of primary photons off electrons and pair creation of photons on atoms. Our ultimate aim is a thorough study of the impact of DM annihilations on the thermal and ionization history of the high-redshift intergalactic medium (IGM) during the dark ages. In addition, a precise determination of the effects of DM decays/annihilations can help constrain its nature. We present the results for some selected DM candidates: (i) a 10-GeV bino-like neutralino; (ii) a heavy DM candidate of rest mass 1 TeV that pair annihilates into muons; and (iii) a 200-GeV wino-like neutralino with a pair annihilation into W+W− pairs. An interface to darksusy allows us to use the computed annihilation spectra in input for our code and follow the complete secondary cascade. The fractional energy depositions into the IGM depend strongly on the DM particle rest mass: whereas for the 10-GeV particle the absorbed energy fraction, in the redshift range 10 < z < 1000, is ≳50 per cent, higher mass candidates deposit their energy less efficiently (∼1–10 per cent), making their impact on the high-z IGM considerably weaker. Noticeably, our approach allows us to consistently follow the low-energy deposition of the cascade products, which can be of interest for a broad range of applications. Finally, we provide both tabulated results and analytical fits that can be readily implemented in theoretical studies of the effects and detectability of the most popular DM candidates.