Some start-ups, like Kick Health, sell blood pressure pills or other prescription drugs for unapproved uses like calming the symptoms of performance anxiety.

One drug, Addyi, which can cause fainting if taken with alcohol, arrived without the necessary safety warning protocols created by the drug’s manufacturer.

Much like Uber, which argues that it is not a transportation company even as it connects drivers and passengers, the drug sites argue that they are tech platforms, not health providers. The sites connect consumers — and often process their payments — to doctors who may prescribe drugs and pharmacies that can ship the medications.

To comply with state laws, the doctors work for separate companies that cater to the sites. The doctors are typically paid for each health consultation, or by the hour, not the number of prescriptions written. The sites generate revenue for themselves by charging service or processing fees to consumers, the doctors or both.

Kick, Roman and Hims each said they complied with laws and did not influence the doctors’ prescribing decisions.

Zachariah Reitano, the chief executive of Ro, the owner of Roman, said his site encouraged people to tend to their health who might not otherwise have done so.

“It provides more convenient, higher-quality, more affordable care for certain conditions and saves people a lot of time and energy,” Mr. Reitano said.