STAGE 4. Selecting the theoretical approach

What steps should be completed?

Step 1: Select the theoretical approach or approaches on which the intervention will be based


What are its bases?

It is based on the premise that people are rational and use any information available to them before adopting a particular behaviour. Therefore, most socially relevant actions are performed voluntarily, so the intention to perform the behaviour is the immediate determinant of the action. This intention depends on the person’s attitude to the behaviour and also on the subjective norm, that is, perception of the social pressure that the person is under to execute the behaviour in question, or not.

Attitudes are based on beliefs, so a person who believes that a behaviour will have positive consequences maintains a positive attitude towards the behaviour but, if they think the consequences will be negative, they will have a negative attitude towards it. An individual’s subjective norms are based on their beliefs about what other people consider that they should or should not do ("normative beliefs"). Individuals usually try to execute a behaviour when they evaluate it positively and believe that people who are important to them expect it to be carried out.

The theory of reasoned action explains the behaviours that are totally under the subject’s control but many behaviours escape from that control to some extent. To overcome this difficulty, the concept of "perceived behavioural control" was added to the original model (approach), formulating the theory of planned behaviour. In this way, the intention to behave in a certain way can be determined by the perceived behavioural control, which can dictate behaviour even beyond the individual’s intention, as well as by attitude and subjective norms.

Which determinants can be addressed?

Attitudes towards drugs and their use, normative beliefs about drug use, the attributions associated with their use, and also environmental determinants, such as regulation of drug use (in particular tobacco and alcohol) or dominant peer group attitudes towards drug use.

Practical implications

These theories emphasise action on the attitudes component, providing information to change beliefs about the consequences of drug use and to promote attitudes against it. It also highlights the importance of modifying the normative beliefs of adolescents and young people about drugs by demonstrating the mechanisms behind social pressure.



Fishbein M & Ajzen I. (1972). Attitudes and opinions. Annual Review of Psychology. 32, 487-544.

Fishbein M & Ajzen I. (1975). Belief, attitude and behaviour: An introduction to theory and research. Reading, MA: Addison-Wesley.

Ajzen I. (1988). Attitudes, personality, and behaviour. Chicago, IL: The Dorsey Press.