Getting a headache and feeling sick are common side-effects for many medicines. Indulging in risky sexual behaviour or pathological gambling - not so common.
Author
- Dipa Kamdar
Senior Lecturer in Pharmacy Practice, Kingston University
But a BBC investigation has highlighted that some drug treatments for restless leg syndrome and Parkinson's disease can lead to such risky behaviour.
Over 150,000 people in the UK live with Parkinson's - a degenerative condition that affects the brain. The main part of their brain that is damaged is the area that produces dopamine, a chemical messenger that regulates movement. Less dopamine in the brain can lead to symptoms such as tremors, muscle stiffness, slow movements and problems with balance.
Another movement disorder is restless legs syndrome (RLS), which affects between 5% and 10% of people in the UK, US and Europe. Twice as many women as men have RLS among those aged over 35.
People with RLS feel they need to uncontrollably move their legs, and may experience a crawling, creeping or tingling sensation in them. Usually, the symptoms are worse at night when dopamine levels tend to be lower. Although the exact cause of RLS is unknown, it has been linked to genes, underlying health conditions, and an imbalance of dopamine.
One of the main treatments for movement disorders is a group of drugs called dopamine-receptor agonists , which include cabergoline, ropinirole, bromocriptine and pramipexole. Dopamine-receptor agonists increase the levels of dopamine in the brain and help regulate movement.
Dopamine is known as the "happy" hormone because it is part of the brain's reward system. When people do something fun or pleasurable, dopamine is released in their brain. But using dopamine-receptor agonist drugs can elevate these feelings, leading to impulsive behaviour.
While common side-effects include headaches, feeling sick and sleepiness, these drugs are also linked with the more unusual side-effect of impulse-control disorders . These include risky sexual behaviour (hypersexuality), pathological gambling, compulsive shopping, and binge eating. Hypersexuality encompasses behaviour such as a stronger-than-usual urge to have sexual activity, or being unable to resist performing a sexual act that may be harmful.
Previous reported cases include a 53-year-old woman taking ropinirole and exhibiting impulsive behaviour such as accessing internet pornography, using sex chat rooms, meeting strangers for sexual intercourse, and compulsive shopping. Another case highlighted a 32-year-old man who, after taking ropinirole, started binge eating and gambling compulsively, such that he lost his life savings.
When the drug was first being prescribed in the early 2000s, it was thought that impulse-control disorders were a rare side-effect associated with these drugs. But in 2007, a UK Medicines and Healthcare Products Regulatory Agency (MHRA) public assessment report advised that "healthcare professionals should warn patients that compulsive behaviour with dopamine agonists may be dose-related".
Between 6% and 17% of people with RLS who take dopamine agonists develop some form of impulse-control disorder, while up to 20% of people living with Parkinson's may experience impulse control disorders.
But the true figures may be even higher, as many some patients may not associate changes in behaviour with their medication, or may be too embarrassed to report it. Case reports show that in most instances, impulsive behaviour stops when the drug is stopped.
Lawsuits
There have been several individual and class-action lawsuits against pharmaceutical companies including GlaxoSmithKline , which produces ReQuip® (ropinirole), and Pfizer , which makes Cabaser® (cabergoline). Patients taking action against these companies claimed they were unaware of these impulsive behaviour side-effects.
For example, in 2012, a French court ordered GlaxoSmithKline to pay £160,000 in damages to Didier Jambart, after he experienced "devastating-side effects" when taking the firm's Parkinson's drug Requip. And in 2014, an Australian federal court approved a settlement against Pfizer for a class-action lawsuit regarding its Parkinson's drug, Cabaser. 150 patients claimed they did not have warning of potential side-effects - including increased gambling, sex addiction and other high-risk activities - of taking Cabaser.
It is now clearer in the patient information leaflets given with all prescribed medication for movement disorders that impulsive behaviour can occur in some patients.
In 2023, the MHRA advised there had been increased reports of pathological gambling with a drug called aripiprazole . This antipsychotic drug, used in the treatment of schizophrenia and mania, partly acts as a dopamine-receptor agonist.
Any drug that increases dopamine levels could theoretically be linked to impulse control disorders, and it is important to keep monitoring patients and their behaviour in such cases.
Not everyone will experience side-effects. Before you begin any course of treatment, your doctor or pharmacist should explain the potential side-effects - but it is also important to read the information leaflet with any medicine. And if you experience any impulsive behaviours with these medicines, speak to your doctor or pharmacist immediately.
Dipa Kamdar does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
