Online mental-health company Cerebral Inc. said it would stop prescribing almost all controlled substances, expanding an overhaul of its treatment practices in the wake of scrutiny over how it provided stimulants for attention-deficit hyperactivity disorder.

Kyle Robertson, Cerebral’s co-founder and chief executive, wrote in an email to staff on Monday afternoon that the company would stop prescribing controlled substances, excluding those in one category, for new patients effective Friday, and for existing patients in October, according to a copy of the email reviewed by The Wall Street Journal. The company said it would seek to taper existing patients off their prescriptions for controlled substances or transfer them out of Cerebral’s care to an in-person clinician.

A Cerebral spokesman confirmed the authenticity of the email, which was reported earlier by Insider.

In his email, Mr. Robertson said that Cerebral had started prescribing controlled substances in 2020 to fill a void created by the inability of patients needing medication to get in-person treatment. He said Cerebral is halting most such prescriptions “due to the evolving landscape around the accessibility of mental-health care, and the ability for patients to return to an in-person or hybrid care model for this treatment.”

The move represents a further retrenchment on controlled substances by Cerebral, which raced to a $4.8 billion valuation by last fall, less than two years after its launch in January 2020. Early this month it said it would pause prescriptions of stimulants to new patients seeking treatment for ADHD, while existing ADHD patients would continue on that medication.

The new step means it will end prescriptions entirely not only for stimulants but also for other controlled substances including benzodiazepines to treat anxiety and some sleep medication.

The email said Cerebral still plans to treat opioid-use disorder with controlled substances, including Suboxone, because the need for such care was too great to be discontinued. Cerebral recently began piloting its online treatment protocol for opiate addiction.

The Journal reported in March that some of Cerebral’s nurse practitioners said they felt pressured by the company to prescribe stimulants and that they felt the company’s 30-minute patient evaluations were too brief to properly diagnose ADHD. Cerebral said at the time that it doesn’t pressure clinicians to prescribe stimulants and that it was providing an essential service in the U.S., where demand for mental-health treatment far outstrips supply.

Some pharmacies have blocked or delayed certain prescriptions from Cerebral prescribers over concerns that the company was writing too many stimulant prescriptions, the Journal reported last month. Cerebral has said prescription delays occurred because of confusion around telehealth policies.

Cerebral said this month that its medical group received a subpoena from the U.S. attorney’s office for the Eastern District of New York as part of an investigation into possible violations of the Controlled Substances Act. The company said it intended to cooperate with the investigation and that no regulatory or law-enforcement authority had accused it of violating any law.

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