Medical marijuana cards are not prescriptions since a prescriptions is controlled by the FDA and they have not approved marijuana cards used at dispensaries.
A pharmaceutical product, Marinol, (Dronabinol) is widely available through prescription. It comes in the form of a pill and is also being studied by researchers for suitability via other delivery methods, such as an inhaler or patch. The active ingredient of Marinol is synthetic THC, which has been found to relieve the nausea and vomiting associated with chemotherapy for cancer patients and to assist with loss of appetite with AIDS patients.
Technically, a marijuana card is not a prescription.