Proposition 64 passes, effective January 1, 2018, a 15 percent excise tax, based on the gross receipts from the retail sale, would be imposed upon retail purchasers of all marijuana and marijuana products, including medical marijuana. In addition, a tax on cultivators of marijuana would be imposed. Patients would not be excluded from these taxes.

The ID card program is voluntary in California; however patients with a doctor’s recommendation only will not qualify for the tax break should Prop. 64 pass.
http://www.canorml.org/news/Tax_Fee_Changes_for_Medical_Marijuana_Patients_upon_Prop._64_Passage