The redesigned study will include only patients from North America, and will exclude mildly psychotic patients, Acadia CEO Uli Hacksell said at the JMP Securities Healthcare Conference.

He said a previous late-stage trial in 2009 failed because of the inclusion of mildly psychotic patients.

"After the results of (the ongoing) study, which we expect will be very good, we will immediately plan for the startup of an identical Phase 3 study," Hacksell said.

The main goal of the ongoing study is to reduce psychotic symptoms in Parkinson's disease patients. The secondary goal is to check tolerability to the drug pimavanserin.

The study will now enhance the main goal, which Hacksell said has already been approved by the U.S. Food and Drug Administration.

The CEO said Acadia will also conduct two additional safety studies, which will roll over patients from the main study.

Hacksell said patients on pimavanserin slept better. There was no worsening of motor symptoms, as often seen in other anti-psychotic drugs. Also, unlike its peers, pimavanserin did not sedate the patient.

The company said it has completed 90 percent of patient enrollment for the late-stage study and it expects to finish enrollment in August.

Apart from Parkinson's, pimavanserin has shown promise in treating psychosis in Alzheimer's disease and as a co-therapeutic with risperidone in schizophrenia.

Acadia said it would stop developing its experimental schizophrenia treatment after the drug failed to meet the goal of an early-stage trial.

Shares of the San Diego, California-based company were down 8 percent at $1.62 on Friday on the Nasdaq.

(Reporting By Pallavi Ail; Editing by Saumyadeb Chakrabarty and Don Sebastian)

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