Publication 61 says
PRESCRIPTION MEDICINES ? Sales of medicines are exempt from sales and use taxes if 1) prescribed for treatment of human beings and dispensed by a registered pharmacist; 2) furnished by or sold to a licensed physician and surgeon, podiatrist, or dentist for patient treatment; 3) furnished by a health facility for patient treatment pursuant to the order of a licensed physician; 4) sold to this state or any political subdivision or municipal corporation for use in treating human beings; 5) dispensed by prescription for the treatment of human beings and furnished without charge by a pharmaceutical manufacturer or distributor to a doctor, a health facility for the treatment of human beings, or to an institution of higher education for instruction or research; 6) furnished by a medical facility or clinic operated by this state or any political subdivision or municipal corporation; or 7) sold to outpatient clinics, as defined under Health and Safety Code 1200, for the treatment of any person pursuant to the order of a licensed physician and surgeon, dentist, and podiatrist. In addition to substances commonly recognized as medicines, the following items are specifically included in the definition of ?medicine?? for sales and use tax purposes:
Some people are advocating legalizing the sale of marijuana -- with a doctor's prescription -- so that the state can collect sales tax on it. But it's a prescription medicine.
Of course, it might be a moot point, because the state can impose license fees, distribution fees, etc that replace the sales tax if the sales tax was deemed unconstitutional.