This post only applies to UK CAA rules.
Whilst the UK CAA public domain website does not have an exhaustive list of allowable drugs, many allowable drugs (which still need to be discussed with your AME) are listed in the guidance notes for individual conditions,
eg for digestive conditions..
Medication used in GI conditions | Medical | Personal Licences and Training
for blood pressure
http://www.caa.co.uk/docs/2499/Hypertension%20FC.pdf
for cardiac rhythm issues
Arrhythmia Medication | Medical | Personal Licences and Training
for psychological/psychiatric issues and sleeping tablets
Centrally Acting Medication | Medical | Personal Licences and Training
and there are more. I suggest you look at the condition you are interested in the medication for and then follow the links here..
Guidance for Medical Certification of aircrew | Medical | Personal Licences and Training
edited to update links and clarify.