Since it is difficult to improve patient compliance to drug prescriptions, an alternative is to select a drug with less consequences for poor compliance, that is, a drug that has the capacity of ’forgiveness’. Forgiveness is the property of a drug which, when compared with another medicine with different pharmacokinetics and/or concentration-effect relationships, blunts the consequences of missing one or two doses in a row, or has a greater variability in the timing of intake. Simulations show that drugs with a concentration-effect relationship modelled with an effect compartment, for example a delayed response, have more forgiveness. A marker of forgiveness would be of some help for doctors deciding which drug to prescribe to patients who are poor compliers.