The study in the journal Menopause looked at health insurance claims of more than 50,000 women.
Those who used estrogen patches were one-third less likely to develop blood clots in the legs or lungs. That's compared to those using estrogen only pills.
Researchers think patches may be less risky because the hormones are delivered through the skin, bypassing the liver.
Also, the patch may not boost clot promoting proteins in the blood.
Researchers say this is study is significant because it is a snapshot of what's going on in the real world.
The study was funded by a hormone patch manufacturer.
