Biogen CEO George Scangos told investors the company’s direct-to-consumer advertising campaign for its multiple-sclerosis drug Tecfidera was designed to address “low awareness” for the drug.

“We were surprised, actually, at the beginning by the low awareness among patients of Tecfidera,” Scangos said during Biogen’s first-quarter earnings call Thursday, “and we had data suggesting that when patients did learn about Tecfidera and went to their physician to discuss it, they often had it prescribed.”

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He added that the ad “did succeed” in raising awareness about Tecfidera even though the drug’s sales missed analysts’ estimates for the quarter. Tecfidera brought in sales of $744 million for the first quarter of 2016, missing analysts estimates of $750 million, however sales are still up 12% from the $648 million the drug brought in during the first quarter of 2015. However, compared to last quarter, Tecfidera sales are down 5%.

Scangos would not say whether that heightened awareness from the DTC campaign translated into more sales. He said the drugmaker plans to give investors an update on the campaign during its next quarterly earnings call.

Low awareness of Tecfidera is surprising given the warm reception it received from neurologists even before the drug had become available, according to a poll conducted by WorldOne Interactive.

Tecfidera was approved in 2013. Trials for the oral drug showed people taking it had fewer MS relapses compared to placebo.

One reason for lower-than-expected sales growth may be that patients have also been dropping off the drug at higher rates than expected, according to Biogen CFO Paul Clancy.

He told analysts that the drug has experienced “higher discontinuation rates than normal,” citing lymphocyte monitoring as a possible reason. The FDA had updated the drug’s label in November 2014 after a patient taking Tecfidera died from a rare brain infection known as progressive multifocal leukoencephalopathy. Clancy said discontinuation rates related to the monitoring requirement are likely to wane now “that the medical education has largely been completed. ”

Still, Scangos said patient demand for Tecfidera in the US was “stable.”