Dopamine stimulators are drugs that mimic the effect of the neurotransmitter dopamine in the brain. Also known as dopamine agonists, these drugs help relieve symptoms of Parkinson’s disease. They also may be used to treat other health concerns, such as tic disorders and certain rare metabolic diseases.

Dopamine is a neurotransmitter that helps regulate body movements and other motor and cognitive functions. Adequate amounts of dopamine in the brain help promote smooth, coordinated movements. Inadequate levels of dopamine triggers symptoms such as tremor, rigidity and bradykinesia (slowness of movement). Dopamine itself is not typically used as a medication because when it is taken orally, it does not cross the blood-brain barrier, and thus cannot be transported into the brain.

In healthy bodies, neurons produce and release dopamine in the brain and other parts of the body. When the dopamine is released by one neuron, it is received by the receptors of the next neuron. This chain reaction eventually leads to the stimulation of nerves.  

Dopamine stimulators cause neuron receptors to react as though they are receiving dopamine, even though there is a deficiency of dopamine in the body. This helps to maintain the chain reaction, which would normally have stopped or slowed down because of the absence of dopamine.

Various neurological disorders can interfere with dopamine production and cause levels in the brain to drop. This may lead to the development of a movement disorder. For example, patients with Parkinson’s disease experience a destruction of dopamine-producing cells. This leads to a sharp decline in dopamine production. By the time 80 percent of these cells are depleted, neurons in the brain begin to behave in an abnormal manner, triggering the symptoms of Parkinson’s.

Dopamine stimulators provide relief from movement disorder symptoms while delaying the onset of certain side effects (e.g., dyskinesias). However, dopamine stimulators may not be as effective as other treatment methods for movement disorders. Levodopa therapy – the combination of levodopa (a dopamine precursor) with other medications – is generally recognized as the most effective treatment method for movement disorders such as Parkinson’s disease. However, there are several drawbacks to levodopa therapy that make it unsuitable for some patients. For example, the side effects of levodopa therapy can be severe for some patients. Additionally, most long-term users of levodopa therapy usually experience a wearing-off effect after a period of time. Dopamine stimulators are less likely to involve this wearing-off effect and, therefore, may be more suitable for patients with mild to moderate movement symptoms.

Dopamine stimulators are often taken in combination with levodopa therapy, but may also be taken on their own. They include:

Apomorphine is the dopamine stimulator that most closely mimics the effects of dopamine. However, this medication cannot be taken in pill form and must be delivered beneath the skin by injection. It begins working within about 10 minutes of being administered, although its effects last only for about 90 minutes. Thus, it is often used as a “rescue therapy” to quickly alleviate symptoms that flare up in patients with movement disorders. Patients sometimes use apomorphine in this way between doses of levodopa.

Cabergoline (brand: Dostinex) is another dopamine stimulator. It has currently been approved for use in the United States for the treatment of hyperprolactinemia (excess milk production in post-partum women). This drug is currently marketed in Europe and elsewhere as a treatment for Parkinson’s disease, where it is taken in a much higher dosage than required for treatment of hyperprolactinemia. There is significant debate among physicians about whether cabergoline should be used to treat Parkinson’s disease in the United States.

Recently, studies have shown that people who are taking pergolide (brand name Permax) or cabergoline as a treatment for Parkinson’s disease may have an increased risk of developing heart valve defects. In March 2007, pergolide was withdrawn from the market upon request by the Food and Drug Administration (FDA). Patients who are concerned about the risks associated with these medications are advised to consult their physician.