When stored as a powder at 4 °C or below, IPTG is stable for 5 years. It is significantly less stable in solution; Sigma recommends storage for no more than a month at room temperature. IPTG is an effective inducer of protein expression in the concentration range of 100 μmol/L to 3.0 mmol/L. , a mutant that over-produces the lac repressor,  is present, then a higher concentration of IPTG may be necessary.
In blue-white screen, IPTG is used together with X-gal. Blue-white screen allows colonies that have been transformed with the recombinant plasmid rather than a non-recombinant one to be identified in cloning experiments.