Haldol decanoate (Haloperidol)

How does it work?

Haldol decanoate injection contains the active ingredient haloperidol, which is a type of medicine called an antipsychotic. It is used in the treatment of various psychiatric illnesses.

When used in psychiatric illness, haloperidol is sometimes described as a neuroleptic or a 'major tranquilliser', though this last term is fairly misleading, as this type of medicine is not just a tranquilliser, and any tranquillising effect is not as important as the main way it works in psychiatric illness.

Haloperidol works by blocking a variety of receptors in the brain, particularly dopamine receptors. Dopamine is a natural compound called a neurotransmitter, and is involved in transmitting messages between brain cells. Dopamine is a neurotransmitter known to be involved in regulating mood and behaviour, amongst other things.

Psychotic illness, and particularly schizophrenia, is considered to be caused by overactivity of dopamine in the brain. Haloperidol blocks the receptors that dopamine acts on and this prevents the overactivity of dopamine in the brain. This helps to control psychotic illness.

Haloperidol improves disturbed thoughts, feelings and behaviour in various mental conditions, including schizophrenia, mania, and behavioural disorders that involve aggression or severe agitation or excitement. It produces a calming effect and controls aggression, delusions and hallucinations.

Haloperidol is used in the long-term management of psychotic conditions such as schizophrenia.

Haldol decanoate is a type of injection called a depot injection. It is administered into the muscle of the buttock, where it forms a reservoir of medicine that is slowly released into the bloodstream over a period of four weeks.

What is it used for?

  • Long-term treatment of schizophrenia and other psychotic illnesses, especially paranoid psychoses.
  • Long-term treatment of other mental or behavioural problems where maintenance treatment is clearly needed.


  • This medicine may cause drowsiness. If affected do not drive or operate machinery. Alcohol should be avoided.
  • Unless your doctor tells you otherwise, you should not suddenly stop treatment with this medicine, even if you feel better and think you don't need it any more. This is because the medicine controls the symptoms of the illness but doesn't actually cure it. This means that if you suddenly stop treatment your symptoms could come back. When treatment with this medicine is stopped, it should usually be done gradually, following the instructions given by your doctor.
  • Your doctor may want to check your heart function with an ECG before you start treatment with this medicine, and may want to do further checks from time to time throughout your treatment.
  • Consult your doctor immediately if you experience abnormal movements, particularly of the face, lips, jaw and tongue, while having treatment with this medicine. These symptoms may be indicative of a side effect known as tardive dyskinesia, and your doctor may ask you to stop treatment, or decrease your dose.
  • Consult your doctor immediately if you experience the following symptoms while being treated with this medicine: high fever, sweating, muscle stiffness, faster breathing and drowsiness or sleepiness. These symptoms may be due to a rare side effect known as the neuroleptic malignant syndrome, and your treatment may need to be stopped.

Use with caution in

  • Elderly people.
  • Liver disease.
  • Kidney failure.
  • Tumour of the adrenal gland (phaeochromocytoma).
  • Thyroid gland problems.
  • Epilepsy.
  • People with conditions that increase the risk of epilepsy or convulsions, eg brain damage or withdrawal from alcohol.
  • Elderly people with dementia (antipsychotic medicines have been shown to increase the risk of stroke in this group of patients).
  • People with risk factors for having a stroke, for example a history of stroke or mini-stroke (TIA), smoking, diabetes, high blood pressure, or a type of irregular heartbeat called atrial fibrillation.
  • People who have had a bleed into the brain (subarachnoid haemorrhage).
  • Heart disease.
  • People with a family history of sudden death due to a heart problem, or a type of abnormal heart rhythm seen on a heart monitoring trace (ECG) as a 'prolonged QT interval'.
  • People with disturbances in the normal levels of salts (electrolytes) in their blood, for example low magnesium or calcium levels.
  • Long-term alcoholism.
  • Malnutrition or starvation.
  • Depression.

Not to be used in

  • Children.
  • Unresponsive unconscious states (comatose states).
  • Reduced awareness, slow reactions or drowsiness due to medicines or illness that reduce activity in the central nervous system.
  • Parkinson's disease.
  • Disorders affecting a specific part of the brain involved in control of movement (basal ganglia), eg Huntington's chorea.
  • Clinically significant heart problems, such as heart failure, recent heart attack, very slow heart rate (bradycardia), 2nd or 3rd degree heart block, or irregular heart beats (arrhythmias).
  • People with a type of abnormal heart rhythm, seen on a heart monitoring trace (ECG) as a 'prolonged QT interval'.
  • People taking medicines that can cause a prolonged QT interval (your doctor will know, but see the end of this factsheet for some examples).
  • People with a history of abnormal heart rhythms originating in the lower chambers of the heart (ventricular arrhythmias, eg Torsades de pointes).
  • People with low levels of potassium in their blood (hypokalaemia).

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

  • The safety of haloperidol for use during pregnancy has not been established. It should be used with caution during pregnancy, and only if the expected benefit to the mother is greater than any possible risk to the foetus. The dose and duration of treatment should be as low and as short as possible. Seek medical advice from your doctor.
  • This medicine passes into breast milk and may potentially have adverse effects on a nursing infant. Mothers who need treatment with this medicine should discuss the risks and benefits of breastfeeding during treatment with their doctor.

Label warnings

  • This medication may cause drowsiness. If affected do not drive or operate machinery. Avoid alcoholic drink.

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here does not mean that all people using this medicine will experience that or any side effect.

  • Redness, swelling or lumps at the injection site.
  • Abnormal movements of the hands, legs, face, neck and tongue, eg tremor, twitching, rigidity, slow movements (extrapyramidal effects).
  • Anxiety, restlessness and agitation (akathisia).
  • Rhythmical involuntary movement of the tongue, face, mouth and jaw, which may sometimes be accompanied by involuntary movements of the arms and legs (tardive dyskinesia - see warning section above).
  • Increased salivation or dry mouth.
  • Feeling mentally dulled or slowed down.
  • Headache.
  • Dizziness.
  • Difficulty sleeping (insomnia).
  • Drowsiness.
  • Disturbances of the gut such as constipation, indigestion, nausea.
  • Loss of appetite.
  • Confusion.
  • Seizures (convulsions).
  • Blurred vision.
  • Excessive sweating.
  • Faster than normal heart beat (tachycardia).
  • Low blood pressure (hypotension).
  • Difficulty passing urine (urinary retention).
  • Sexual problems, such as erectile dysfunction.
  • High blood prolactin (milk producing hormone) level (hyperprolactinaemia). Sometimes this can lead to symptoms such as breast enlargement, production of milk and stopping of menstrual periods.
  • High temperature combined with falling levels of consciousness, paleness, sweating and a fast heart beat (neuroleptic malignant syndrome). Requires stopping the medicine and immediate medical treatment - see warning section above.
  • Uncontrolled rolling of the eyes and neck (oculogyric crisis). Requires immediate treatment.
  • Abnormal heart beats (arrhythmias).
  • Skin reactions, such as rashes, itching, increased sensitivity to sunlight.
  • Liver problems.
  • Disturbances in the normal numbers of blood cells in the blood.

The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while being treated with this one, to ensure that the combination is safe.

There may be an increased risk of drowsiness and sedation if haloperidol is used with any of the following (which can also cause drowsiness):

  • alcohol
  • barbiturates, eg amobarbital, phenobarbital
  • benzodiazepines, eg diazepam, temazepam
  • indometacin
  • MAOI antidepressants, eg phenelzine
  • sedating antihistamines, eg chlorphenamine, hydroxyzine
  • sleeping tablets, eg zopiclone
  • strong opioid painkillers, eg morphine, codeine, dihydrocodeine
  • tricyclic antidepressants, eg amitriptyline.

Medicines that increase the risk of a type of abnormal heart rhythm, seen as a 'prolonged QT interval' on an ECG, should not be taken in combination with haloperidol. These medicines include the following:

  • antiarrhythmics (medicines to treat abnormal heart beats), eg amiodarone, procainamide, disopyramide, sotalol
  • the antihistamines astemizole, mizolastine or terfenadine
  • atomoxetine
  • certain antidepressants, eg amitriptyline, imipramine, maprotiline
  • certain antimalarials, eg halofantrine, chloroquine, quinine, mefloquine, Riamet
  • certain other antipsychotics, eg thioridazine, chlorpromazine, sertindole
  • cisapride
  • intravenous erythromycin or pentamidine
  • moxifloxacin.

There may also be an increased risk of a prolonged QT interval if medicines that can alter the levels of salts such as potassium or magnesium in the blood, eg diuretics such as furosemide, are taken in combination with haloperidol.

This medicine may enhance the blood pressure-lowering effects of certain medicines used to treat high blood pressure (antihypertensives). If you are taking medicines for high blood pressure you should tell your doctor if you feel dizzy or faint after starting treatment with this medicine, as your blood pressure medicines may need adjusting.

Haloperidol may reduce the blood pressure lowering effect of guanethidine.

Haloperidol may oppose the effect of levodopa and medicines for Parkinson's disease that work by stimulating dopamine receptors in the brain, for example ropinirole, pergolide, bromocriptine.

Haloperidol may oppose the effect of anticonvulsant medicines used to treat epilepsy.

Haloperidol should be used with caution in people taking lithium, as this combination may possibly increase the risk of side effects. If you are taking these medicines together, your blood level of lithium should be monitored regularly. You should consult your doctor straight away if you notice any new side effects, particularly an unexplained fever, or if you become confused or disorientated, with a headache, disturbances of balance and drowsiness.

The following medicines may increase the breakdown of haloperidol by the liver, which could make it less effective. If you are prescribed any of these medicines, your doctor may need to increase your dose of haloperidol:

  • carbamazepine (in addition, haloperidol may increase the blood level of carbamazepine, which could increase the risk of its side effects)
  • phenobarbital
  • phenytoin
  • rifampicin.

The following medicines may increase the blood level of haloperidol, which could increase the risk of its side effects. If you are prescribed any of these medicines, your doctor may need to decrease your dose of haloperidol:

  • buspirone
  • fluoxetine
  • fluvoxamine
  • quinidine
  • venlafaxine.

The Haldol decanoate depot form of haloperidol should not be used in combination with clozapine.

Other medicines containing the same active ingredient

Dozic Haldol Serenace

Haloperidol tablets are also available without a brand name, ie as the generic medicine.