Given that antagonism of D2 receptors is more beneficial on the positive symptoms of schizophrenia and antagonism of 5-HT2 receptors on the negative symptoms, this characteristic underlies haloperidols greater effect on delusions, hallucinations and other manifestations of psychosis. Haloperidols negligible affinity for histamine H1 receptors and muscarinic M1 acetylcholine receptors yields an antipsychotic with a lower incidence of sedation, weight gain, and orthostatic hypotension though having higher rates of treatment emergent extrapyramidal symptoms. Haloperidol acts on these receptors: (Ki)

D1 (silent antagonist) – Unknown efficiency
D5 (silent antagonist) – Unknown efficiency
D2 (inverse agonist) – 0.7 nM
D3 (inverse agonist) – 0.2 nM
D4 (inverse agonist) – 5–9 nM
σ1 (irreversible inactivation by haloperidol metabolite HPP+) –  3 nM
σ2 (agonist): 54 nM
5HT1A receptor agonist –  1927 nM
5HT2A (silent antagonist) –  53 nM
5HT2C (silent antagonist) – 10,000 nM
5HT6 (silent antagonist) – 3666 nM
5HT7 (irreversible silent antagonist) – 377.2 nM
H1 (silent antagonist) – 1,800 nM
M1 (silent antagonist) – 10,000 nM
α1A (silent antagonist) – 12 nM
α2A (silent antagonist) – 1130 nM
α2B (silent antagonist) – 480 nM
α2C (silent antagonist) – 550 nM
NR1/NR2B subunit containing NMDA receptor (antagonist; ifenprodil site): IC50 – 2,000 nM

Pharmacokinetics
By mouth
The bioavailability of oral haloperidol ranges from 60 to 70%. However, there is a wide variance in reported mean Tmax and T1/2 in different studies, ranging from 1.7 to 6.1 hours and 14.5 to 36.7 hours respectively. Intramuscular injections
The drug is well and rapidly absorbed with a high bioavailability when injected intramuscularly. The Tmax is 20 minutes in healthy individuals and 33.8 minutes in patients with schizophrenia.
The depot forms are not suitable for initial treatment, but are suitable for patients who have demonstrated inconsistency with oral dosages.The decanoate ester of haloperidol (haloperidol decanoate, trade names Haldol decanoate, Halomonth, Neoperidole) has a much longer duration of action, so is often used in people known to be noncompliant with oral medication. A dose is given by intramuscular injection once every two to four weeks. The IUPAC name of haloperidol decanoate is [4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]piperidin-4-yl] decanoate. Topical formulations of haloperidol should not be used as treatment for nausea because research does not indicate this therapy is more effective than alternatives. Adverse effects
Sources for the following lists of adverse effects:As haloperidol is a high-potency typical antipsychotic, it tends to produce significant extrapyramidal side effects. According to a 2013 meta-analysis of the comparative efficacy and tolerability of 15 antipsychotic drugs it was the most prone of the 15 for causing extrapyramidal side effects.With more than 6 months of use 14 percent of users gain weight. Haloperidol may be neurotoxic.Common (>1% incidence)

Extrapyramidal side effects including:
Akathisia (motor restlessness)
Dystonia (continuous spasms and muscle contractions)
Muscle rigidity
Parkinsonism (characteristic symptoms such as rigidity)
Hypotension
Anticholinergic side effects such as: (These adverse effects are less common than with lower-potency typical antipsychotics, such as chlorpromazine and thioridazine.) Blurred vision
Constipation
Dry mouth
Somnolence (which is not a particularly prominent side effect, as is supported by the results of the aforementioned meta-analysis.