True estrogen (like estradiol) is a regulated prescription drug in the U.S. and cannot be bought over the counter. You can obtain it through: Over-the-Counter Estrogen: Safety & Effectiveness - Hers
Buying estrogen involves a clear distinction between (which requires a doctor) and over-the-counter (OTC) supplements (which contain plant-based mimics). 1. Where to Buy Prescription Estrogen (Hormone Therapy) where to buy estrogen supplements