The most common side effect repoed with treatment with haloperidol is:

Haloperidol is a high potency antipsychotic and extra pyramidal disturbances (Akathasia, Acute dystonia, Parkinsonism) are the major/most common repoed side effects associated with its use. Ref: Essentials of Pharmacology by KD Tripathi, 5th Edition, Page 377; The Evidence-Based Guide to Antipsychotic Medications edited by Anthony J. Rothschild, 2010, Page 176; Kaplan and Sadock's Psychiatry, 9th Edition, Page 1055.