The multi-part identifier could not be bound

I guess you'll have to include patient_meds in the table list as:

FROM psychotropes, patient_meds

You are not including the table in the query. Without knowing the schema this is just an assumption. Also a database diagram does nothing to assist in queries.

SELECT ax_dose
FROM psychotropes
INNER JOIN patient_meds ON psychotropes.psychotrope_name = patient_meds.psychotrope
WHERE (patient_meds.patient_id = 12)