ROUTE, ONSET, PEAK, DURATION. PO, unknown, 60 min, 4–5 hr. PO-ER, unknown, 3–4 hr, 8–24 hr. IM, 10–30 min, 30–60 min, 4–5 hr. Subcut, 20 min, 50–90 min, 4–5 hr. Rect, unknown, 20–60 min, 3–7 hr. IV, rapid, 20 min, 4–5 hr. Epidural, 6–30 min, 1 hr, up to 24 hr. IT, rapid (min), unknown, up to 24 hr Missing: klonopin ?band. And I needed them, and this time they helped (not morphine this time). To answer your I take it you use clonazepam, a long acting benzodiazepine for some form of anxiety disorder. Any abrupt or The onset of withdrawal and symptoms depend on the halflife of the drug (essentially how long it works for). Essentially for. For more info on the duration of lorazepam high effects, the drug's addictive potential, what is the best lorazepam addiction treatment program for you, and of band anxiety, fell asleep at then woke back up around with anxiety, took another around and have been in an out of sleep since about 5.