The placebo effect is a treatment or ingested substance that the patient or person believes will make him/her well, when in fact the treatment is effectively inert. The placebo effect is attributed to the effects cited by antidepressants and the cures by witch doctors, to name a few. What do we do, then, when the placebo effect - the positive effect of belief - is observed in psychotherapy?
The answer is clear. Identify the greater good and allow it to continue. The greater good is the overall benefit against the possible risk. One example is a patient who used dabs of WD-40 on his sore knees that was followed by relief. While I do not know of the possible benefits of such an unusual home remedy, I cannot deny him the opportunity to experience the benefit of pain relief. The same approach may hold true for antidepressants if not for the long-term impact from down regulation of serotonin production, creating the need for antidepressants for many to escape pain.
The power of belief needs to apply to behaviors that do not have the long-term negative effects. For example, a belief in La Llorona does not carry a long-term effect in avoiding streams or rivers. But a belief that small doses or arsenic will cause hair growth is not a belief that will lead to better health.
In therapy, evaluate the overall beneficial and emotional effect. If the following questions you ask yourself are 'Yes' then it is more likely the placebo should not be sabotaged.
1. Does the person report an improvement in subjective happiness?
2. Does the person identify the substance, object, movement, chemical as the source of their improvement?
3. Is the substance, object, movement, chemical unlikely to cause a physical or mental problem?
4. Does the substance, object, movement, or chemical isolated to the individual taking or using it and does not involve anyone else?
5. Does the substance, movement, object, or chemical's use unlikely to cause financial and economic problems?
If all are answered yes, then the benefit of the placebo likely outweighs the potential harm. In legal parlance, you will likely be exercising reasonable care.