For the diagnosis to be made, auditory and visual hallucinations cannot be prominent, though olfactory or tactile hallucinations related to the content of the delusion may be present. The delusions cannot be due to the effects of a drug, medication, or general medical condition, and delusional disorder cannot be diagnosed in an individual previously properly diagnosed with schizophrenia. A person with delusional disorder may be high functioning in daily life. Recent and comprehensive meta-analyses of scientific studies point to an association between a deterioration in aspects of IQ in psychotic patients, in particular perceptual reasoning.