Abstract: The present invention relates to a method of preventing or reducing one or more adverse post-anaesthetic effects in a patient, comprising treating the patient with low level laser therapy (LLLT) prior to anaesthesia and/or during anaesthesia and/or following anaesthesia, and to a method for assessing whether a patient is at risk of suffering from adverse post-anaesthetic effects, comprising determining whether the patient contains a polymorphism in a gene encoding one of the following proteins: (a) protein associated with assembly and disassembly of microtubules; (b)ion channel protein; (c) membrane stability protein; (d) Melanocortin systems proteins; (e) proteins associated with Alzheimer's and/or Parkinson's vulnerability; or (f) proteins associated with migraine.