Does phentermine thin your blood?

Phentermine is a stimulant that is similar to an amphetamine. It is an appetite suppressant that affects the central nervous system.

Phentermine is used together with diet, exercise and behavioral modification to treat obesity (excessively overweight) in people with risk factors such as high blood pressure, high cholesterol, or diabetes.

Read more: https://www.drugs.com/phentermine.html#ixzz0td1dgW5x

Blood thinning has not been reported, however you could double check with the doc/pharmacist who prescribed the med, hope this helps?