A medication taken for purposes other than those for which it is approved by the U.S. Food and Drug Administration (FDA). Off-label use of medications is a very common and accepted practice throughout medicine. It is particularly common in neurologic diseases because they tend to be less common, and, therefore, drug companies are unlikely to invest the enormous resources required to obtain FDA approval for another on-label use of a drug they can already sell on the market. The effectiveness and safety of common off-label uses are typically well supported by clinical studies in the scientific literature. Some off label uses are so commonplace that many physicians don’t even think of them as off-label unless they happen to review the insert on a medication. Quite a number of medications taken to control various symptoms of Parkinson’s disease have off-label uses. It is important that the person taking an off-label drug fully understand the expected benefits and possible side effects of the drug. Typically off-label drug use involves trying the medication to treat similar symptoms in a different condition, such as using acetylcholinesterase inhibitor medications approved for use to improve cognitive function in people with Alzheimer’s disease as a therapy to improve cognitive function of people with Parkinson’s disease. Although the symptoms of cognitive impairment appear similar in these two conditions, they arise from different pathological conditions (physiological and neurochemical causes). Other off-label uses may involve using dosages that are different from those approved or in combination with other medications.
Often off-label medication use evolves through anecdotal reports of its effectiveness. As a result, the off-label use may become an approved use, as occurred with amantadine, which started its pharmaceutical life as an antiviral medication to prevent or shorten the course of influenza A and is now an approved and effective dopaminergic medication used as monotherapy in de novo parkin-son’s and early-onset Parkinson’s and as one of the adjunct therapies in middle-to-late stage Parkinson’s to alleviate dyskinesias. Influenza is a particular health risk among older people, who also are more likely to have neurodegenerative diseases such as Parkinson’s. Doctors noticed that their older patients who had Parkinson’s disease and took amantadine to head off influenza also experienced dramatic improvement in their Parkinson’s symptoms. Open-label use of amantadine to control the symptoms of Parkinson’s spread, eventually leading to clinical research trials that confirmed the drug’s effectiveness as an anti-Parkinson’s medication.