Osmolex ER (amantadine) for Parkinson’s disease
Fact-checked by Joana Carvalho, PhDWhat is Osmolex ER for Parkinson’s disease?
Osmolex ER (amantadine) was an approved oral therapy used to treat Parkinson’s disease and drug-induced movement problems known as extrapyramidal reactions in adults.
The therapy was available as extended-release (ER) tablets taken once daily in the morning. The brand-name medication was discontinued in the U.S., and no generic version of Osmolex ER is available.
Parkinson’s disease develops as nerve cells that produce dopamine, an important chemical messenger involved in controlling movement, become damaged and die. While it was not fully understood how Osmolex ER helped control Parkinson’s symptoms, it was believed to affect dopamine signaling.
Amantadine, Osmolex ER’s active ingredient, is also the active ingredient in Gocovri, a therapy approved to manage involuntary movements and off episodes in people with Parkinson’s disease. Although Osmolex ER and Gocovri share the same active ingredient, they have different formulations and are not interchangeable.
Supernus Pharmaceuticals, the company marketing Osmolex ER, notified the U.S. Food and Drug Administration (FDA) in December 2023 that manufacturing of Osmolex ER had been discontinued, and distribution ceased on April 1, 2024. A specific reason for ending manufacturing was not disclosed. The FDA formally withdrew Osmolex ER’s approval in September 2025.
Although Osmolex ER is no longer marketed, immediate-release amantadine generics are still available in the U.S. in various formulations.
The most common Osmolex ER side effects included nausea, dizziness or lightheadedness, and insomnia.
Therapy snapshot
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| Treatment name | Osmolex ER |
| Administration | Extended-release tablets |
| Clinical testing | Previously approved in the U.S., but its distribution ceased in 2024, and FDA approval was formally withdrawn in 2025. |
Osmolex ER in Parkinson’s disease clinical trials
Osmolex ER’s approval was supported by studies showing that the extended-release tablets provided amantadine exposure bioequivalent to that of immediate-release formulations.
Three randomized Phase 1 studies evaluated Osmolex ER in healthy adults. Their results showed that:
- Osmolex ER released amantadine more gradually than immediate-release amantadine. With repeated once-daily dosing, blood levels peaked about 7.5 hours after the morning dose, or around the middle of the day.
- When taken once daily, Osmolex ER provided similar overall amantadine exposure as an immediate-release syrup formulation taken twice daily at half the dose per administration.
- A high-fat meal did not affect how much amantadine from Osmolex ER reached the bloodstream.
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