AstraZeneca said on Wednesday its blood-thinning drug Brilinta failed to help stroke patients as hoped in a major clinical trial, dealing a blow to a product viewed as an important driver of future sales and profits.

The trial found that Brilinta was not significantly better than aspirin, the current standard of care, in preventing recurrent attacks in the 90 days after patients suffer a stroke.

In a clinical trial dubbed Socrates, Brilinta taken twice daily was compared to a once- daily dose of aspirin in patients with two forms of stroke.

Those taking the drug had fewer heart attacks, other stroke or death, but the difference wasn’t statistically significant, the London-based company said in a statement Wednesday.

Chief executive Pascal Soriot has identified Brilinta as critical to reaching $45 billion in annual revenue by 2023, a goal set in 2014 as AstraZeneca fended off a takeover attempt by Pfizer .

The anti-clotting medicine is sold as a treatment after heart attacks, but AstraZeneca is conducting studies intended to expand the population of patients who can take the pill.