Most importantly : to abandon the idea that consciousness is a sort of arbiter capable of deciding the outcome of the conflict between two ideas. Consciousness is a playground for our mental representations. Their fusion gives us this homogeneous « I » impression only because there is no mental retro-control over consciousness to split the elements involved in the fusion. Why in this case do we perceive the discontinuities of our consciousness, the different « small voices » that inhabit it? Because they win in turn a temporary celebrity, depending on the context and the sequence of previous ideas.
When two contradictory ideas come into play on the conscious battlefield, other mental schemas are capable of representing the thing. They are very specific to the prefrontal cortex and I call them « the Observer » because this term explicitly refers to what they are capable of doing: they allow you to observe your own mental functioning and influence it. It is a retro-control and not an authoritarian ‘decision-maker’. If it had the power to direct everything, you would not have had to ask your question.
The Observer is a late capacity of our mental maturation. Its varying effectiveness separates the people who take the train of their life running and those who choose the destination. How should it intervene in a situation like yours?
In the first place it is necessary to establish whether the two ideas are really contradictory. Most of the time they each have their own interest, which makes them useful in certain circumstances. An idea, even appearing stupid to the majority of people, always has a utilitarian background, which must be identified. It is thus possible to extract two contradictory ideas from his personal library, when the time is right for each one. Human existence is a fuzzy logic.
In your case the two ideas clearly do not have the same origin. One is the emergence of a physical demand. Your body claims quick and easy satisfaction that is that of the drug. These are the most difficult ideas to ignore. They are indeed directly acting. It is the drug that takes control of your behavior. The rest of the occupants of consciousness attend the affair vaguely embarrassed. The other idea is much less owner. That drug use is a slow mental and social suicide is a foreign observation. It is not yet properly integrated in you because, simply, the drug has settled before it and has permanently imprinted your neurological patterns. Its contradiction is difficult to establish, especially since it brings no immediate pleasure. It only satisfies the general opinion that surrounds you. It satisfies the projection you have of your future self rid of the drug, yet you must be able to extract yourself from the present. You are in the dilemma of the child who is offered two sweets after an hour if he manages not to touch the first one he has before his eyes. At the age of five, half of the children succeed. Will you be able to trust this future self and refuse immediate pleasure?
The method is simple. It is not a « conscience that must resist the temptation of drugs ». It is a new self that does not include drugs. You have to get it out of your identity. Look at it every time it presents itself as an alien who wants to take control of your brain. The other representations of your conscience must regroup before this invasion and proclaim « Drug, you are not part of us! Go and spread your misery elsewhere ». To be effective, these acting representations must give you maximum satisfaction. Find drug substitutes. Go running, dance… cook? Sublimate your desire in an occupation that values you. Take responsibility for helping someone else. There are always worse off than self.