how long does a single dose of inderal work?

Inderal (or scientific name propranolol) is rapidly and completely absorbed, with peak plasma levels achieved approximately 1–3 hours after ingestion. Half life is 3 -4 hrs for the parent compound and 5- 7.5 for active ingredient. The duration of action of a single oral dose is longer than the half-life and may be up to 12 hours, if the single dose is high enough (e.g., 80 mg).
N.B: half life is the period the drug take to half its concentration in plasma.