Medicinal cannabis has proven therapeutic benefits and doctors should be able to prescribe it, the government’s chief medical adviser has said.

In the first part of an evidence review ordered by the home secretary, Sajid Javid, Professor Dame Sally Davies recommended medicinal cannabis should be moved out of schedule one – a group of drugs considered to have no medical purposes that cannot be legally possessed or prescribed,

Dame Sally’s comments, published on Tuesday, are the first time the government has formally acknowledged that cannabis can have health benefits.

“There is now … conclusive evidence of the therapeutic benefit of cannabis-based medicinal products for certain medical conditions and reasonable evidence of therapeutic benefit in several other medical conditions,” Dame Sally said.

“I therefore recommend that the whole class of cannabis-based medicinal products be moved out of schedule one.”

The change would allow the drugs to “be prescribed under controlled conditions by registered practitioners for medical benefit”, she continued.

It would also help improve the evidence base for research into the drugs, she said, “maximising benefits to patients”.

Cannabis can currently be used for research purposes in the UK, but a licence is needed.

Dame Sally later said in a statement it was “now clear that from a scientific point of view keeping cannabis-based medicinal products in schedule one is very difficult to defend”.

She added: “Let me be emphatic – this report does not look at recreational cannabis use and does not endorse or condone recreational use.

“There is well-established evidence on the potential harm of recreational cannabis use. This is about helping patients, in exceptional circumstances, get access to treatment which could work.”

The home secretary said he would wait for a second part of the review to be completed before considering taking action.

Commissioned on Tuesday, the second part of the review will be completed by the Advisory Council on the Misuse of Drugs (ACMD).

Mr Javid ordered the review into the scheduling of medicinal cannabis after the issue was thrust to the forefront by the cases of severely epileptic children Alfie Dingley and Billy Caldwell.

Six-year-old Alfie has a genetic condition that causes clusters of seizures of up to 30 a day that has proved unresponsive to almost all medications – but when his mother Hannah Deacon took him to Holland, she discovered three drops of cannabis oil a day dramatically reduced the frequency of his fits.

After a months of campaigning by the family, they were granted a licence to treat Alfie with the drug.

Cannabis oil also appeared the only treatment for 12-year-old Billy’s epilepsy, but his mother had the drug confiscated from her at Heathrow.

Billy was granted a 20-day emergency licence in June that allowed him to possess the drug, but not before he suffered multiple seizures and was admitted to hospital in a critical condition.

Alfie and Billy are among around 20,000 children living with epilepsy who do not respond to medication currently available on the NHS.

The home secretary said: “Recent cases involving sick children made it clear to me that we needed to take a fresh look at the scheduling of cannabis-related medicinal products.

“I would like to thank the chief medical advisor for her initial review and have now asked my independent advisory committee to commence the second stage of this process.

“When I have received its advice I will consider what next steps need to be taken.”

The home secretary stressed that the government has no plans to legalise cannabis. Recreational use of cannabis will remain illegal and the penalties for unauthorised supply and possession will remain unchanged, the government said.

A number of medical experts welcomed Dame Sally’s findings.

Prof David Nutt, the Edmond J Safra chair and head of the Centre for Neuropsychopharmacology at Imperial College London, and founder of DrugScience, responded by saying: “At last!”

Dr Adrian James, a registrar at the Royal College of Psychiatrists, said: “We fully support a review that may lead to improved treatment for patients.

“Cannabis products for medicinal use that have been properly reviewed, and approved by the National Institute for Health and Care Excellence, can have significant health benefits.

“While it is for the government and voters to decide if recreational cannabis should be legal, as mental health doctors we can say with absolute certainty that its use carries severe risks for some, including psychosis, depression and anxiety.”

The prime minister’s official spokesman said: “Prof Dame Sally Davies examined existing research into therapeutic and medicinal benefits of cannabis-related products.

“This has led today to the commissioning of the second part of the review that will be completed by the Advisory Council on the Misuse of Drugs.

“The ACMD will be advising on whether cannabis-related medicinal products should be rescheduled within the next three weeks.”

NHS at 70: Pride and worry as free health service celebrates birthday Show all 18 1 /18 NHS at 70: Pride and worry as free health service celebrates birthday NHS at 70: Pride and worry as free health service celebrates birthday Nurses test the hearing of a newborn child Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday The waiting room is busy in Milton Keynes University Hospital Reuters NHS at 70: Pride and worry as free health service celebrates birthday On Ward 24, two nurses work at the nurses station Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday In A&E, a porter rushes a patient through the corridor Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday A surgical team prepares a patient for their operation Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday In the physiotherapy department, patients are treated in the hydrotherapy pool Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday On Ward 8, an inpatient awaits visitors Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday In the physiotherapy department, amputees take a class Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday A junior doctor is at work in the staff room Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday A surgical team prepares a patient for their operation Reuters NHS at 70: Pride and worry as free health service celebrates birthday An inpatient has her hair washed by the staff hairdressers Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday In the audiology department, a mother watches on as her son is given a hearing test Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday On Ward 8, staff serve lunch to the patients Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday On Ward 24, a patient waits on their bed Reuters NHS at 70: Pride and worry as free health service celebrates birthday On Ward 8, a cleaner is at work Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday A nurse takes blood from a patient Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday On Ward 8, an inpatient receives a visitor Reuters/Hannah McKay NHS at 70: Pride and worry as free health service celebrates birthday Inpatient Donald Ritson lies in bed in Ward 24 in Milton Keynes University Hospital Reuters

Genevieve Edwards, from the MS Society, said: “This is significant news. We’re delighted that the chief medical officer recognises the evidence that cannabis can effectively manage MS symptoms. Critically, she also rightly acknowledges the dangers of uncontrolled street cannabis.