The U.S. Food and Drug Administration (FDA) has said the asthma medication Xolair may elevate the risk of stroke and related medical problems.

Xolair (omalizumab) is designed to treat asthma and certain other chronic allergic reactions. The drug is specifically designed for patients that cannot, or should not, take steroids.

For most patients with severe asthma, a class of drugs called corticosteroids can help control the condition. However, steroids suppress the immune system, and in some cases they simply do not work. Drugs like Xolair carry different risks than steroids, but may work for patients who haven’t found steroids effective or worth the side effects.

However, FDA research has found that patients taking Xolair had a slightly higher risk of developing blood and blood vessel problems. In particular, the study found evidence of “transient ischemic attacks,” or TIAs, as well as heart attack, chest pain, high blood pressure in the blood vessels that feed the lungs, and blood clots. All of these disorders can be related to blockages in blood vessels.

Since the FDA only had observational data, the agency pulled in 25 double-blind clinical trials to augment their data. With these additional resources, the researchers were able to observe the same increase in a more controlled trial.

However, these double-blind studies were shorter term, weakening the new data. At the same time, the FDA looked for an increased risk of cancer with Xolair, but was unable to find any.

However, the FDA’s statement indicated that the same limitations that prevented a more definitive statement on the risk of clot-related medical problems also prevent them from more definitely saying that the drug cannot increase the risk of cancer.

Based on the studies, the FDA has decided to add warnings to the drug information that comes with Xolair. Based on the data, the new statements state that there could be a somewhat elevated risk of blood clots, phrased as a “slightly elevated risk of cardiovascular and cerebrovascular serious adverse events.” The FDA also mentioned that there is an “uncertain findings” regarding a possible cancer risk.