A senior MP leading an all-party group looking at medical cannabis has called the existing laws "bizarre and cruel".
Sir Mike Penning MP has called for "fundamental reform" of the system.
"Medical cannabis is a health issue, not a misuse of drugs issue," Sir Mike said in a statement. "It's about patients and relieving suffering."
It follows the home secretary's decision to grant 12-year-old Billy Caldwell temporary access to cannabis oil medication to treat his epilepsy.
Mr Penning, who is the proposed chairman of the new All Party Parliamentary Group (APPG) on Medical Cannabis Under Prescription, said: "It's bizarre and cruel that we have a system that allows the medical use of strong opiates, but bars the medical use of cannabis.
"The current structures within government on this issue are not fit for purpose. We need to move this from criminal justice to health."
He said he supported reclassifying cannabis under the law so it would be regarded as having a medicinal use.
Last Monday officials at Heathrow airport confiscated Billy's cannabis oil, which his mother Charlotte uses to treat his severe epileptic seizures.
She had been attempting to bring a supply into the UK from Canada.
Ms Caldwell says her son's seizures dramatically reduce when he takes the oil, which contains a substance called Tetrahydrocannabinol (THC) that is illegal in the UK.
Following the confiscation, Billy was admitted to hospital in London after his seizures "intensified".
His condition led to Home Secretary Sajid Javid later approving the return of some of the cannabis oil, after doctors made clear it was a medical emergency.
The Home Office has granted a limited licence for the drug to be administered to the child in hospital for 20 days.
Billy's case has prompted a renewed debate on the legislation surrounding medical cannabis.
Sir Mike said many more families needed "urgent" access to medical cannabis, adding that the medical use of cannabis was "totally separate from recreational use".
Does cannabis have medicinal benefits?
CBD and Tetrahydrocannabinol (THC) are two types of cannabinoids found naturally in the resin of the marijuana plant.
A cannabis-based drug called Sativex has been licensed in the UK to treat MS. It contains THC and CBD.
Doctors could, in theory, prescribe it for other things outside of this licence, but at their own risk.
MS patients prescribed Sativex, who resupply it to other people, also face prosecution.
Another licensed treatment is Nabilone. It contains an artificial version of THC and can be given to cancer patients to help relieve nausea during chemotherapy.
Source: NHS Choices
Sir Mike is one of a growing number of MPs from all parties who support the reform of the laws regarding the medicinal use of cannabis and cannabis products.
Fellow Conservative Crispin Blunt MP, co-chair of the all-party parliamentary group on drug policy reform, said the existing law was "frankly absurd".
Ex-Tory health minister Dan Poulter said the current situation was "ridiculous" and pledged to push for a change in the law.
Former drugs minister Norman Baker, a Liberal Democrat, has described the confiscation as "cruel and inhumane", and renewed calls for a law change citing cannabis's "useful medical properties".
But UCL's Dr Michael Bloomfield said the use of medical marijuana is "far from straightforward". He said in some jurisdictions the drug's use for medical conditions is "a potential way of decriminalising cannabis through the back door".
Many other countries, including much of the US, Germany, Italy and the Netherlands, have legalised the substance's use medicinally.