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Risperidone is an atypical antipsychotic, and of all the substances in this group it acts particularly strongly on the dopamine system. Both things follow from that: a reliable antipsychotic effect with a comparatively favourable metabolic profile, but also dose-dependent extrapyramidal symptoms and a marked rise in the hormone prolactin. It was also the first substance in its group to be available as a depot injection on a two-weekly cycle.
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Because risperidone acts so forcefully on the dopamine system, that also affects the movement system — technically, extrapyramidal symptoms (EPS). They are clearly dose-dependent: rare at low doses, increasing as the dose rises.²
| Form | How it feels | When it typically appears |
|---|---|---|
| Akathisia | An agonising inner urge to move, an inability to sit still, constant pacing up and down | Usually in the first few weeks or after a dose increase |
| Acute dystonia (early dyskinesia) | Sudden involuntary muscle contractions, for instance of the tongue, neck or eyes | Very early, often in the first few days; particularly in younger people |
| Drug-induced parkinsonism | Tremor, muscle stiffness, small shuffling steps, reduced facial expression | After weeks to months, dose-dependent |
| Tardive dyskinesia | Involuntary movements around the mouth and face | Only after a longer period of treatment |
Akathisia is the most distressing movement disorder and at the same time the most frequently misread. People affected describe it as an unbearable inner restlessness that movement relieves only briefly. From the outside it looks like nervousness or anxiety and is easily interpreted as a worsening of the illness — with opposite consequences, because with akathisia a dose increase would be exactly the wrong move.
The decisive clue is the timing: if the restlessness begins shortly after treatment starts or after a dose increase and was not there before, that points to a side effect. Note such observations down with the date.
What helps: above all a dose adjustment, alongside specific medicinal options and, if necessary, a switch to an antipsychotic that is easier on motor function — all of it under medical direction.
Risperidone was the first atypical antipsychotic with a long-acting injection. The drug sits inside tiny microspheres from which it is released over days to weeks. The injection is given every 14 days into the muscle, by healthcare professionals.¹
Switching over is not a simple swap: the depot does not work immediately, and release from the microspheres only really gets going after about three weeks. That is why oral treatment is continued for that period after the first injection — the so-called overlap.
Before a changeover, the substance is as a rule first tried as a tablet so that tolerability is known — a depot cannot be removed from the body again. The decision is made by the treating practice together with you; it is not a compulsion but one of several equally valid options.
| Combination | Consequence | What to do |
|---|---|---|
| Strong CYP2D6 inhibitors, above all the antidepressants paroxetine and fluoxetine | Breakdown is slowed and the amount of risperidone in the blood rises — more extrapyramidal symptoms and dizziness | Only under medical supervision; the dose is often adjusted |
| Enzyme inducers such as carbamazepine, rifampicin or St John's wort | Breakdown is speeded up and the effect can wear off | Watch the effect; do not take herbal remedies without checking first |
| Blood pressure lowering medicines | A stronger drop in blood pressure, particularly while the dose is being settled | Stand up slowly, check blood pressure |
| Other sedating agents (tranquillisers, sleeping tablets, opioids) | Cumulative tiredness, impaired reactions | Assess the overall picture rather than each preparation on its own |
| Medicines that prolong the QT interval on the ECG | An increased risk of cardiac arrhythmia | Show your full medication list, have an ECG if needed |
| Parkinson's medicines (levodopa, dopamine agonists) | Mutual weakening of effect | Only after specialist consideration |
| Alcohol | Increased tiredness and a stronger drop in blood pressure | Avoid while the dose is being settled, be cautious in general |
The commonest case is the combination with an antidepressant. Risperidone is converted by the liver enzyme CYP2D6 into its active metabolite; if that enzyme is inhibited — which paroxetine and fluoxetine do markedly — the amount of risperidone in the blood rises. The combination is not forbidden, but it does need to be managed deliberately, often with an adjusted dose. Check such combinations in the guide to drug interactions; on alcohol, the guide medications and alcohol is worth reading.
On top of that: some people naturally use CYP2D6 more slowly and react more noticeably even to low doses. That explains part of the differences in tolerability — and argues for taking side effects seriously even at a dose that is "actually low".
Older age. Treatment starts lower and is increased more slowly: the drop in blood pressure when standing up considerably raises the risk of falls, and extrapyramidal symptoms occur more readily. If you take several medicines, it is worth looking at medications in old age and polypharmacy.
Kidney function. Here risperidone is more sensitive than many other antipsychotics: the active metabolite is excreted mainly through the kidneys and accumulates if kidney function is impaired — on the same tablet dose, the actual amount of drug rises. With chronic kidney disease the dose is therefore lower. General points can be found under medications for kidney and liver disease.
Bipolar disorder. Alongside schizophrenia, risperidone is licensed for the treatment of moderate to severe manic episodes in bipolar disorder — here too for as short a time as possible and with regular review.⁴
Pregnancy and breastfeeding. Risperidone is among the comparatively well-studied antipsychotics; on current knowledge a markedly increased risk of malformations has not been established. After use in the final third of pregnancy, temporary adaptation problems are possible in the newborn. An existing treatment is not stopped abruptly, because an untreated relapse is usually the greater risk; the assessment is made by the treating practice, with Embryotox providing the specialist basis.⁵ One point to note: a raised prolactin level can change the cycle so much that a pregnancy goes unnoticed at first. The guide medications during pregnancy gives you your bearings.
Stopping suddenly brings two risks at once, which overlap and are hard to tell apart:
With the depot, the drug fades away by itself over weeks after the last injection. That is no substitute for planning — a cancelled depot with nothing in its place is an unsupervised stop on a delay. A documented record of doses, appointments and complaints shows whether a change really is connected with the reduction.
That is quite possible and one of the commonest prolactin-related effects. It can be clarified with a blood test measuring the prolactin level. Just as important: an absent period does not rule out pregnancy, and the cycle can also start again while you are on risperidone — raise both. If a raised level is confirmed, there are ways forward: a dose adjustment, a change of substance or deliberate monitoring. Do not stop the medicine yourself to "test whether that is where it comes from".
Akathisia is more likely — a dose-dependent side effect that shows itself as an agonising inner urge to move. The most important clue is the timing: if the restlessness began shortly after treatment started or after a dose increase and was not there before, that points to the side effect. This matters because the consequences are opposite: with a worsening of the illness more medicine might be right, whereas with akathisia that would be exactly wrong. Get in touch promptly instead of putting up with it.
No. The depot is a dosage form, not a control measure. Many people actively choose it, because one appointment every two weeks is more of a relief than 14 tablets you have to think about every day — and it also gives steadier drug levels. Conversely, the tablet is not the poorer choice: it can be adjusted and stopped faster. Both are equally valid options, and you help decide between them.
Note restlessness, your cycle or dizziness with the date — that makes the conversation at your appointment concrete.
