Cannabis products will be available for prescription by doctors to patients from November 1, it has been announced.
Sajid Javid rescheduled the products, relaxing rules around the circumstances in which they can be given out, after considering expert advice.
The new regulations will apply to England, Wales and Scotland.
Alfie's mother, Hannah Deacon, was one of many campaigners to welcome the move.
She said: "Today is a momentous day for every patient and family with a suffering child who wish to access medicinal cannabis.
"We urge the medical world to get behind these reforms so they can help the tens of thousands of people who are in urgent need of help."
An initial review by chief medical adviser Dame Sally Davies concluded that there was evidence medicinal cannabis has therapeutic benefits.
The Advisory Council on the Misuse of Drugs (ACMD), which carried out the second part of the review, then said doctors should be able to prescribe medicinal cannabis provided products meet safety standards.
It recommended cannabis-derived medicinal products should be placed in Schedule 2 of the Misuse of Drugs Regulations 2001.
Cannabis has previously been classed as a Schedule 1 drug, meaning it is thought to have no therapeutic value but can be used for the purposes of research with a Home Office licence.
Mr Javid said that to constitute a cannabis-based product for medicinal use, three requirements must be satisfied.
These are that it "needs to be a preparation or product which contains cannabis, cannabis resin, cannabinol or a cannabinol derivative; it is produced for medicinal use in humans and; is a medicinal product, or a substance or preparation for use as an ingredient of, or in the production of an ingredient of, a medicinal product".
Professor Mike Barnes, the medical cannabis expert who secured the first long-term licence for its use for Alfie, said: "This announcement has transformed the position of the UK in this exciting and developing field.
"Many of my medical colleagues are understandably unsure about the benefits.
"After all, medical cannabis has been illegal in the UK for generations. But I urge them to embrace these developments.
"Compared to many pharmaceutical drugs, whole plant medical cannabis products are remarkably safe and, as recent high-profile cases have shown, can produce dramatic improvements for patients."
Setting out the new regulations, Mr Javid said: "This brings these products explicitly into the existing medicines framework.
"These regulations are not an end in themselves. The ACMD will be conducting a long-term review of cannabis and the National Institute for Health and Care Excellence (NICE) has been commissioned to provide advice for clinicians by October next year.
"The Government will monitor the impact of the policy closely as the evidence-base develops and review when the ACMD provides its final advice."