Done’s rival Cerebral Inc. said earlier this year that its medical group had received a grand-jury subpoena from the Justice Department looking into possible violations of the Controlled Substances Act.

Cerebral said in May it would cease prescribing most controlled substances after it received its subpoena. The company said it hadn’t been accused of violating any laws and that it was cooperating with the investigation.

The Justice Department probe is being led by the DEA’s Diversion Control Division, whose agents made inquiries to Done and Cerebral, according to the people and documents reviewed by the Journal. The unit aims to stop potentially illicit use of legally manufactured drugs. The DEA is a law-enforcement agency within the Justice Department.

Done said in a statement that it hasn’t received any notifications from the DEA or any other federal agency regarding an investigation, request for records or preservation of documents and that it is committed to providing high-quality psychiatric care while complying with all applicable laws and regulations. A DEA spokeswoman declined to comment. A Cerebral spokesman declined to comment. The Justice Department declined to comment.

The Journal first reported in March that some of Done’s clinicians felt they were pressured to prescribe stimulants and that a 2021 internal company report written by Done’s then-chief medical officer said that “multiple Done providers have specifically expressed a perception of pressure to diagnose ADHD and prescribe stimulants.”

Done has said it relies on its clinicians to use their judgment and follow proper procedures and that the internal report was irrelevant to its business.

Done’s prescribing practices were also featured in a Journal article in August about a Los Angeles man with a history of abusing drugs who relapsed after a Done clinician prescribed him Adderall despite evidence of his addiction in a state database. The man later died of a drug overdose. The toxicology report cited acute opiate and cocaine intoxication as his cause of death.

Done declined to comment about the patient, citing privacy restrictions.

A federal law requires doctors to conduct at least one in-person appointment with a patient before prescribing them a controlled substance like Adderall. After the onset of the pandemic, the government made an exception to that law while the Covid public-health emergency remains in effect, and some telehealth companies like Cerebral, Done and a handful of others availed themselves of it to offer ADHD treatment that could include a controlled-substances prescription.

Done is among the last telehealth companies that continues to prescribe stimulants online after Cerebral said it would stop doing so and a rival online ADHD treatment service, Ahead, was shut down by its parent company, Truepill Inc. Truepill said it shut down Ahead because it wasn’t a part of Truepill’s core mail-order pharmacy business.

The Journal also reviewed a copy of a subpoena sent to another telehealth startup asking the company to provide a list of its clinicians. After the company told a DEA representative that it has a policy against prescribing controlled substances, the DEA said it would close its file on the company, according to a copy of an email the DEA sent that the Journal also reviewed.

DEA agents have also continued to interview former Cerebral employees in recent months, according to people familiar with the interviews. They have asked about whether clinicians were pressured to prescribe and for details about the company’s relationship with Truepill, Cerebral’s preferred pharmacy through which it encouraged clinicians to fill prescriptions, said these people. Truepill said in May it would temporarily halt prescriptions for Schedule II controlled substances like Adderall.

Truepill said in a statement that patient safety continues to be its top priority and that it currently isn’t filling prescriptions for any controlled substances prescribed via telemedicine while it evaluates next steps.

The Journal also previously reported that some Cerebral clinicians felt pressured to prescribe stimulants. Cerebral said at the time that it doesn’t pressure clinicians to prescribe medication and that it provides an essential service at a time when demand for mental-health services outpaces supply.

Write to Rolfe Winkler at rolfe.winkler@wsj.com