The neurotransmitter dopamine is part of many necessary body functions, including memory, movement, motivation, and the “reward” system in our brain that’s activated when we experience things like eating our favorite ice cream or scrolling through social media.

In people with Parkinson’s disease (PD), changes in the brain lead to a deficiency of dopamine, which in turn causes many of the symptoms of the disease, including tremor, rigidity, and impaired balance and coordination.

The most common drug treatment for Parkinson’s is a combination of the drugs levodopa and carbidopa — often referred to as just levodopa or L-dopa — which is converted to dopamine in the brain.

Another class of drugs that is often used to treat PD is called dopamine agonists. These medications work by stimulating the parts of the brain that are influenced by dopamine, in essence “tricking” the brain into thinking it’s getting enough of the neurotransmitter, according to the Parkinson’s Foundation.

Dopamine agonists are used to help with movement issues, and they are not as potent as carbidopa-levodopa and may be less likely to cause dyskinesias (involuntary movements) as a side effect, per the Foundation.

But although these medications can be very helpful in treating PD symptoms, in some people, they can cause serious side effects, including impulse control disorders (ICDs), or unwanted behaviors.

What Behaviors Are Most Common in ICDs in Parkinson’s?

Any behavior could be an impulse control behavior, says Margaret Ferris, MD, clinical assistant professor of neurology at Stanford Medicine who specializes in treating movement disorders, including Parkinson’s disease, at Stanford Health Care, both in Palo Alto, California.

“We define it as a behavior that someone is unable to control or stop, even though it is causing them or their relationships harm or could cause them or their relationships harm,” says Dr. Ferris.

The most common behaviors are obsessive or excessive gambling; obsessive or excessive shopping, particularly online shopping; hypersexuality, which is excessive sexual behavior or obsession with sex; hoarding behaviors; and overusing the internet on computers or phones, she says.

Those types of problems show up the most and are the most damaging in terms of consequences, but impulsive behaviors can also be things like a person obsessively working in their garden or on their house, says Ferris. “Even if they are putting their health at risk — for example, climbing up a ladder to clean a gutter — they are unable to stop themselves.”

How Common Are ICDs?

“It’s estimated that anywhere between 4 and 14 percent of people on these medications can develop this kind of disorder,” says Ferris. These types of behaviors have also been described in people on levodopa or other Parkinson’s disease medications — mostly at high doses — but the link is not as strong, she says.

What Are the Potential Consequences?

Unlike most other side effects of medications, ICDs can have a very direct impact the family and friends of the patient, says Ferris. “If they’re over-shopping or gambling, it really can get serious: People can lose their entire retirement savings. Hypersexuality can also be a big issue. The person might go out and cheat on a spouse whom they love and have been with for a very long time,” she says.

Ferris emphasizes that ICDs are a side effect of the medication, and the person isn’t doing the impulse behavior deliberately.

“But it can have long-lasting effects on relationships; it can particularly put marriages at risk. I’ve seen patients who ended up getting divorced because of issues with these kinds of behaviors,” she says.

How Parkinson’s Medications Can Cause ICDs

The exact mechanism behind the link between dopamine agonists and compulsive behaviors is not fully understood, says Ferris. “It’s thought that the drugs can overstimulate the dopamine receptors so that the reward system in the brain doesn’t function as it normally would,” she says.

Ferris gives the example of eating sugar: “It tastes good, you like it, and so you eat more. Eventually, you eat too much, and you stop getting a reward from it. You no longer want to eat it, so you put it away. But in a person with ICD, that negative feedback system that’s part of the reward system is not operating as it should,” she says.

Risk Factors for Developing Impulse Control Disorder

There isn’t any test or way to know for certain if a person with Parkinson’s will develop an impulse behavior if they are prescribed a dopamine agonist, but there are risk factors that appear to make it more likely, says Ferris.

“Younger people and males are at higher risk for impulse control disorders, and so young men are at the highest risk,” she says. A history of risky behavior, past issues with addiction, smoking, sleep issues, depression, and anxiety are also among the risk factors, according to a paper published in August 2021 in Current Opinion in Neurology.

Just because someone has one or more risk factors doesn’t necessarily mean that they can’t be prescribed a dopamine agonist, says Ferris. “It’s up to the patient and the provider’s discretion. There are some providers who don’t feel as comfortable prescribing these medications to younger men,” she says.

“If a person has multiple risk factors — for example, a young man who is a current smoker with a strong history of alcohol and drug abuse, and a gambling problem in the past — as a provider, I would be unlikely to prescribe one of these medications in this case. But as with any medication, it’s about the risk versus the benefit. Talking with the patient and family so that they are aware of the potential risks is very important,” says Ferris.

People May Try to Hide Their Behaviors From Loved Ones

One thing that makes ICDs especially difficult is that patients are often reluctant to admit that these behaviors are happening, because their brain is getting a reward from the behavior, says Ferris.

“It’s giving them pleasure to do these things specifically, and so sometimes the patient is very hesitant to admit that these behaviors are happening. This isn’t a cognitive issue — they understand that it’s hurting themselves or their relationships — they’re just not able to stop because of the way their brain is working. They will often hide their behaviors from their family and their doctor,” she says.

How Are Impulse Control Disorders Managed?

When ICDs develop, the medication must be reduced, discontinued, or switched to another dopaminergic drug, according to a review published in the Expert Review of Neurotherapeutics.

If the person must be taken off the medications because of these behaviors, the drug must be tapered down slowly, and the patient should be monitored, says Ferris. “There’s something called dopamine withdrawal syndrome, which can be very miserable for people. They can get depressed, they can even become suicidal at times. Not everyone gets the withdrawal symptoms, but it’s a real thing,” she says.

There is evidence to suggest that dopamine agonists that are delivered via transdermal patch may have a lower risk of causing ICDs, perhaps because there is less fluctuation in how much of the drug is being delivered, says Ferris.

Open Communication and Family Involvement Is Important

Patients and their families need to be aware of the side effects of these medications, including the risk for ICDs, says Ferris.

Having family members attend appointments can be useful for several reasons: It can keep the lines of communication open and even to help the patient remember other things the doctor says during the visit, she says.

“It’s also important for patients to let doctors know whether they are okay with their physician speaking with their spouse. Establishing that relationship can be helpful if a family member notices something but doesn’t know how to bring it up with the patient directly, then they can bring it up with their doctor,” says Ferris.

Sharing bank accounts and retirement information can help the spouse or partner know if there are any big changes, she says. “Try to maintain a level of trust,” says Ferris, “You don’t want them to feel that they are always being checked up on, but pay attention, and be aware of the risks for ICDs.”