Our primary objective is to assess the effects of self-formulated conditional plans to change the health-related behaviours of health consumers and healthcare professionals. Our secondary objective is to explore if the effects of self-formulated conditional plans are modified by: (i) the form of the plan (e.g., implementation intention, action plan, coping plan); (ii) fidelity to plan development (did the individual participate in its development as planned?); and, (iii) complexity of the targeted behaviour (e.g., number of actions required; regularity of the behaviour).