In an interview on Medicinal Marijuana

And this book is Therapeutic Uses of Cannabis by the British Medical Association. 

This book by the BMA was the first one which listed a number of pathologies (only where there is scientific evidence) that could be responsive to cannabis therapy. This list ranges from vomiting and nausea caused by chemotherapy, muscular spasticity, a need for appetite stimulation and therapy against pain. 

The final conclusion of the BMA study was absolutely favourable towards the use of therapeutic cannabis and this was the first time that such an authoritative medical body had pronounced so clearly in favour of the treatment. This scientific evaluation gave a significant boost to the whole debate and led to more detailed research into the subject of the endogen cannabinoid system. A huge quantity of research has accumulated over the last 20 years, much of which has not ended up in book form, particularly the research undertaken by the Italian group led by Vincenzo Di Marzo, an international leader in medicinal cannabis research. This group has demonstrated how the presence in our system of cannabinoid receptors and physiological mediators have the characteristics of a system that governs multiple physiological functions, from the control of the appetite, to the control of muscular mobility, from the control of pain, to the control of convulsions, all things which give significant rational support to the therapeutic use of cannabinoids. 

There is still a great deal of resistance to therapeutic cannabis though. 

People who are against the legalisation of medicinal cannabis are usually against the idea because they apply the prejudices that they hold toward cannabis as a recreational drug when evaluating cannabis as a medicine. Their stance is more political than scientific. From a scientific point of view, if you are against a particular therapy it is because you have weighed up the pros and cons in clinical tests and made a rational judgment about its efficacy. 

Is there a negative side to this treatment? 

The negative side effects of medicinal cannabis is a very delicate subject, especially when you are talking about using cannabis in psychiatric disorders, even though there are indications that it could be used in anti-anxiety therapy or as part of anti-psychotic treatment. The problem is that there is the potential danger that these symptoms could be accentuated rather than alleviated by the use of therapeutic cannabis.