"I have considerable sympathy for the family of Mr Renton who face an incredibly difficult situation. Understandably they want to do the best for their son, and they believe that this option is worth trying.
"I have also considered the absence of any other treatment options, the low risk of significant adverse effects, and the conclusion reached by the hospital ethics committee from an individual patient perspective.
"Ministerial approval in this case does not extend beyond Mr Renton's application and should in no way be construed as setting a wider precedent," he said.
Mr Dunne said the advice he has received was that there remains a lack of clinical evidence supporting the use of CBD products in sufferers of Mr Renton's condition.
"The fact that Elixinol does not have a supporting pharmaceutical testing regime means this application has been reviewed as a stand-alone case and weighed against the severity of his condition.
"I hope for a positive outcome for Mr Renton and his family," Mr Dunne said.