Two new cholesterol-fighting drugs show great promise in reducing the risk of strokes and heart attacks, but scientists say they need to conduct further research to ascertain safety of the drugs and long-term clinical effects.

The drugs -- evolocumab, being developed by Amgen, and aliracumab from Sanofi and Regeneron-- are in a class of drugs known as PCSK9 inhibitors.

They would be offered under the brand names Repatha for the Amgen drug and Praluent for the Sanofi or Regeneron version.

Both drugs have displayed an impressive ability to lower LDL or "bad" cholesterol by as much as 62 percent but there have been some signs of adverse neurocognitive effects that may complicate the pharmaceutical companies' task of securing Food and Drug Administration (FDA) approval, experts say.

Those effects included mild confusion or forgetfulness, observed in less than 1 percent of patients. There were also some issues with muscle pain and eye problems, researchers reported.

Both drugs are intended for use when cholesterol levels in patients given the maximum tolerable dosage of statin drugs, such as Pfizer Inc.'s Lipitor, can't be brought down into a healthy range.

If FDA approval is secured, the Sanofi and Regeneron drug could be on the market by June, analysts say, while Amgen has a target of August for its drug.

Pfizer is reported to be working on a similar drug, although it is still in the early stages of development.

Results of clinical trials on both of the new drugs have been published in the New England Journal of Medicine.

In the trials, all of the participants were on statins; half then were additionally given either evolocumab or alirocumab every two to four weeks, while the other half were given a placebo.

After one year, LDL level in the PCSK9 groups were 60 percent lower, researchers said.

"Among people treated with evolocumab, the average LDL after one year of treatment was 48 milligrams per deciliter of blood, the lowest LDL ever seen in the experimental arm of a lipid-lowering trial," said Dr. Marc Sabatine, a professor of medicine at Brigham and Women's Hospital in Boston, who acted as principle investigator in two of the trials.

In an editorial accompanying the published studies, Neil Stone and Donald Lloyd-Jones - who served as co-authors of recent cholesterol guidelines - said they looked forward to "further results that show cardiovascular benefit and documented safety."

However, they cautioned, "it would be premature to endorse these drugs for widespread use before the ongoing randomized trials ... are available."