The practice of " polypharmacy," or the use of a large number of ingredients in prescriptions, which was common in the middle ages, was greatly due to the view enunciated by Alkekendo, and held by one of the Arabian schools of medicine: that the activity of medicine increases in a duplicate ratio when compounded with others; and it was only in the first half of the 18th century that the practice was altogether discontinued in the pharmacopoeias, although the theory was shown to be incorrect by Averroes in the 12th century.
It is highly important to observe that the official doses of the various pharmacopoeias may with safety be greatly exceeded in practice.
Oxycedrus, from the Mediterranean district and Madeira, yields cedar-oil which is official in most of the European pharmacopoeias, but not in that of Britain.
The study of pharmacological actions was at first almost entirely confined to those of remedial agents, and especially to the remedies in the different national pharmacopoeias, but in many cases it has now been extended to substances which are not used for curative purposes.
Cannabis indica - as the drug is termed in the pharmacopoeias - may be given as an extract (dose 4-1 gr.) or tincture (dose 5-15 minims) .