biological approach in psychology

i've learnt that a limitation of the biological approach is that: explanations are often correlational, e.g. explanations of mental disorders are based on evidence demonstrating the relationships of drug treatments and symptoms. it makes assumptions and this method can not be used to establish cause and effect.
I don't understand this at all?? can someone maybe put it into context for me or explain it and give me an example, thank you so much in advance!!

Basically the way i think of it it is that the biological approach makes assumptions like if you have a headache and you take paracetamol your headache feels better, so the biological approach would assume that it is a lack of paracetamol that caused the headache (which is obviously not true!). The biological approach makes assumptions like this without taking into account that there could be something else causing the headache (like stress), and because their methods are correlational there's no way of knowing

thanks i think i understand it a bit more thanks to your analogy. could you give me an example of a method in the biological approach that is correlational and therefore cant establish cause and effect?

the explanation provided isn't great tbh -- the biological approach would say that bc paracetamol reduces pain and works by inhibiting the enzyme involved in the production of prostaglandins, the headache was caused by the production of this enzyme in the first place. but we know this might not necessarily be true bc headaches are often caused by stress or fatigue and paracetamol isn't always effective in treating them, hence why we could say that explanation is correlational.

in terms of an example directly linked to psychology, you could use the biological explanation for schizophrenia. studies have been done on schizophrenic patients that found many of them have enlarged cerebral ventricles in their brains, and the biological approach has attributed this to being a cause of the disorder. however, this is correlational bc there is no way to prove that the ventricles didn't just become enlarged after the onset of schizophrenia, rather than the other way around (i.e they could be a symptom instead of a cause).