What does “double effect” mean in drug therapy?

Morphine, benzodiazepines, and other palliative medications may be associated with a “double effect.” This means that while these medications provide symptom relief, they may also shorten the patient’s remaining lifespan. A reduction in life expectancy due to palliative medications is possible when respiratory function is already severely impaired by ALS and the sedative effect of the medication causes a further decline in respiratory function. In this situation, the medications can cause drowsiness (sedation) and increase the body’s own accumulation of carbon dioxide (carbon dioxide narcosis). In this way, palliative medications can accelerate the dying process, which would have occurred at a slightly later time without medication.

Before starting treatment with palliative medications (e.g., morphine and benzodiazepines), patients and their families should be informed about and counseled on the potential dual effect.