Yes we do. For quite some effects seen in patients in psychiatry it's not too hard to come up with a drug which induces similar experiences. Take paranoia for instance. And hallucinations of course. Or, to mention an extreme and very rare example: there are people lacking a certain connection between the low-level visual processing and the parts translating that to known objects (sorry, don't remember exact terminology). It's extremely hard to imagine, but such people have normal vision yet they do not recognize based on what they see. E.g. they see a chair, but don't know it is a 'chair'. However when they touch the chair they know 'aha, chair'. Someone I know described that exactly once when on psychdelics; psilocybin IIRC.