Does anyone know how long the side effects of haldol (haloperidol) can last?

Depends: Depends on what side effects. Tardive dyskinesia which may occur after being on any antipsychotic for an extended period of time is potentially irreversible. All other side effects should go away within 2 or 3 weeks. As with all medications it is always a matter of weighing the benefits vs the risks.

Haldol (haloperidol) side effects: Complicated answer, because there's great variability between individuals in the metabolism of haldol (haloperidol). Also it depends on whether you're asking about immediate effects, or more long term ones like tardive dyskinesia -- which unfortunately can persist indefinitely. Women are more susceptible to this result. Immediate dyskinesias can remit quickly. Other effects may be intermediate, lasting days.

Haldol (haloperidol): Temporary side-effects such as tremors and muscle spasms resolve with treatment, permanent ones such as tardive dyskinesias persist and can occur after years of use.