Propranolol usually starts to work within about 30 minutes to 2 hours after taking an immediate-release dose. The peak effects, when the medication reaches its highest level in the blood, occur between 1 to 6 hours depending on the formulation. For anxiety, people often feel the calming physical effects such as reduced heart rate, less shaking, and sweating within 1 to 2 hours. Extended-release propranolol takes longer to start working but its effects last longer. Its half-life ranges from about 3 to 10 hours depending on the form, so the medication may need to be taken multiple times a day if immediate-release or once daily if extended-release.