Mechanism of action
Phentermine plays a role in regulating hormones related to your fight or flight response, including epinephrine, norepinephrine, and dopamine. For example, phentermine acts on the central nervous system (CNS) to initiate the production of norepinephrine in the hypothalamus. Doing such helps to control your appetite. It also works via a secondary mechanism in which it helps to move fat via stimulation of the CNS and adrenal glands4.
In terms of cardiovascular side effects, phentermine can cause increased blood pressure, an elevated heart rate, and palpitations. It can also cause anxiety, a tingling sensation in your feet or hands, trouble sleeping, and constipation2.