Two big drug companies, Bristol Myers Squibb and Johnson & Johnson, have stopped a major study on a new experimental blood thinner called milvexian. This study was testing if milvexian, along with usual medicines, could prevent heart problems better than the usual medicines alone in people who recently had a heart attack. The study was stopped early because it seemed unlikely that milvexian would work better. However, the companies still believe milvexian could be a very successful drug and are continuing two other large studies. This setback is part of a series of challenges for Bristol Myers Squibb, which has also had difficulties with other drugs this year. Milvexian is part of a new class of drugs called Factor XIa inhibitors, which are hoped to be safer than widely used blood thinners like Eliquis and Xarelto. The stopped study was supposed to include 16,000 people who would take either milvexian or a placebo along with standard treatments. The goal was to see if milvexian could reduce the risk of heart attacks, strokes, or death from heart problems. The companies did not share detailed results, but they mentioned that treating heart problems is complex and more research is needed. The other two studies, which are testing milvexian for preventing strokes and treating an irregular heartbeat called atrial fibrillation, will continue. Other companies like Novartis and Regeneron are also developing similar drugs and are watching milvexian’s progress closely.