Just because someone is under the influence of drugs and/or speaking incoherently doesn't mean they are not speaking truth.
Some drugs, like psychedelics and entheogens, can clarify as opposed to obscure the mind, as the very words 'psychedelic' and 'entheogen' suggest. Cultures have known this for millennia and therefore practiced drug use in controlled settings - unlike modern day recreational drug users who use mind-altering substances like toys.
It is drug ab-use that leads to negative consequences not drug use per se.
Similarly, just because someone is mentally ill doesn't mean that some of their utterances are not based in reality including their own, even though oddly interpreted and discomforting to common understanding.