The Food and Drug Administration has put on clinical hold a trial aiming to assess a switch of impotence drug Cialis from prescription-only to over-the-counter status, Sanofi said Monday.

The French drugmaker’s announcement notes that the hold is “due to matters surrounding the protocol design” of the actual use trial (AUT), which has yet to recruit any patients, and that it’s working with regulators to move the Cialis program forward. 

Sanofi’s pursuit of a non-prescription form of the erectile-dysfunction drug dates back to 2014, when developer Eli Lilly granted it the rights to OTC Cialis. The drug was earmarked to become a backbone of Sanofi’s consumer healthcare division, which it formed in 2019, and a contributor to helping the division outpace the market in the 2024 timeframe, Reuters points out.

Before allowing an Rx-to-OTC switch to take place, the FDA assesses whether consumers are able to use the drug safely without a prescription, which requires grasping the nuances of the condition at hand. Cialis, for instance, is contraindicated in patients taking a class of heart drugs called nitrates due to the potential for a dangerous drop in blood pressure. 

Cialis (tadalafil), first approved by the European Medicines Agency in 2002 and then by the FDA in 2003, has since gained approval in 120 countries. The drug’s indications have grown beyond ED to include signs and symptoms of benign prostatic hyperplasia (BPH). 

Cialis’s annual global sales reached $2.16 billion in 2013, with total worldwide revenue exceeding $14 billion since launch. To date, more than 45 million men worldwide have been treated with the drug.

Cialis wouldn’t be Sanofi’s first successful Rx-to-OTC switch. In 2011, allergy drug Allegra (fexofenadine) got the OTC nod.