Dopamine is a neurotransmitter secreted from the substantia nigra, a small region in the brainstem that withers away in Parkinson’s disease. As natural dopamine levels in the brain begin to fall, signs of Parkinson’s disease appear. If dopamine is replaced, many of the symptoms improve.
One would think, then, that dopamine should be given as soon as possible. There are other options, though. In addition to given dopamine directly (a drug called carbidopa-levodopa), Parkinson’s disease patients may benefit from a class of drugs called dopamine agonists.
These are drugs that aren’t dopamine but have similar effects on the nervous system. Some physicians have argued that dopamine agonists should be used earlier in the disease course and that only elderly patients with at least moderate disability should receive levodopa.
Levodopa is the most effective medication there is to treat Parkinson’s symptoms. That said, it’s not without side effects.
One of the fears of levodopa use is that it can cause excessive movement called dyskinesia. People with dyskinesia have a writhing movement that is out of their control. While it looks uncomfortable, however, most with dyskinesia prefer it to parkinsonism, and studies suggest that dyskinesia ultimately doesn’t have much an impact on quality of life.
Some researchers have suggested that dopamine may actually accelerate the disease course while patching over the symptoms.
More research has not supported this view, however.
Symptoms may fluctuate while on dopamine, meaning there may be times of the day where tremor, rigidity, and slow movements are less well controlled than others. On the other hand, it’s unclear how those fluctuations actually impact quality of life.
Furthermore, people on other medications like dopamine agonists may also eventually have fluctuations.
Other arguments in support of early use of levodopa say that it will improve quality of life early in the disease course, the importance of which has not been given sufficient attention. Levodopa is also considerably less expensive than dopamine agonists.
Drug companies are no longer promoting the use of levodopa because there are so many generic forms. In other words, there are financial motivators for pharmaceutical companies to promote the use of other, more expensive medications early in Parkinson’s disease, rather than relying on the old, tried-and-true levodopa, and this may influence the choices of prescribing physicians.