How long does it take haldal to work?

Dosing type. It depends on how Haldol (haloperidol) is given, how quickly it works. Its sedative activity can be quite quick, especially when given intravenously. Actual antipsychotic effect may take a few days, with increasing improvement over several weeks.
Several weeks. It may take several weeks for oral Haldol (haloperidol) to take effect in your body, depending on the dose taken and the consistency of the adherence to the treatment regimen. For Haldol (haloperidol) decanoate im which is an intramuscular injection given every 4 weeks, it may take 4-5 months to reach a steady state level in your body.