Medical marijuana patients are only allowed to purchase their medicinal cannabis from licensed dispensaries. You will pick your dispensary when you're ready to purchase your prescription. So far, the state has registered 3 dispensaries:
Fluent (formerly Cansortium Texas)
Adam Sharon - Communications Director
Compassionate Cultivation
Morris Denton
goodblend (Surterra Texas LLC, d/b/a goodblend)
Marcus Ruark