Molecular gas depletion time (or the inverse of the star formation efficiency), i.e. the ratio of the CO luminosity to the infrared luminosity or the corresponding molecular gas mass with the CO-to-H₂ conversion factor α_CO = 5 M_⊙ (K km s⁻¹ pc²)⁻¹ to the SFR as a function of metallicity. GRB hosts are marked with full red circles or red arrows with vertical bars showing the errors. The symbols of other galaxies are indicated in the legend and described in Sect. 2.4. The solid black line is our fit to the non-GRB galaxies (Eq. (3)), whereas the dashed black line is the relation found by Hunt et al. (2015). GRB hosts are consistent with other galaxies (see Sect. 3.2).