“It’s incredibly problematic, because health care providers in general are considered very trustworthy,” Ms. Patten said. “And especially by their followers, who are looking for their expertise.”

In an interview, Dr. Devgan said it was standard practice for pharmaceutical companies to cover her expenses to medical meetings, and she did not think it was necessary to disclose this. She said she would not favor Jeuveau over competitors, and noted that she said as much in her video. “I’m always trying, with my social media and traditional media presence, to be very neutral,” she said.

Dr. Petro said she traveled to Cancun to learn about the product and came away impressed. She said she didn’t think she was endorsing Jeuveau, but would consider disclosing to followers that Evolus had paid for her trip. “I never would want to be dishonest with them,” she said.

David Moatazedi, the Evolus chief executive, said in an interview that the Cancun event was a standard advisory board meeting, similar to those that the company’s competitors hold, and that the doctors were not paid or given incentives to promote the company. The company also noted that the doctors sometimes used the hashtags of competing products, like #botox, in their posts.

However, Mr. Moatazedi did say the company offered doctors what he called “social media moments,” like the Evolus-themed runway or a confetti-throwing station.

“We wanted to make the break periods of this meeting productive as well for doctors, and many of them like to inform their patients around the newest technologies,” Mr. Moatazedi said.

To Wall Street investors, Evolus has pitched its unconventional approach as a way to distinguish its product from Botox, made by Allergan, which commands about 70 percent of the more than $1 billion market for wrinkle-smoothing injections. Jeuveau, which was approved by the Food and Drug Administration in February, is Evolus’s only product.