The MHRA has published a hierarchy for the use of unlicensed medicines:

• First choice should be a product that is licensed in the UK for the patient’s particular clinical needs, if it is available.
• Second choice should be product that is licensed in the UK, albeit not for the indication the patient requires it. This is because many aspects of the license will hold good, for example, it will be clear that the product meets certain standards of quality and the side effect and interaction profiles will be well known. This is referred to as using a medicine “off label”, and increases the responsibility and potential liability of the prescriber.
• Third choice – assuming a UK-licensed product cannot meet the patient’s need, either within or outside its license – is that a medicinal product licensed outside the UK may be imported for use by the patient. 
• Fourth choice, and assuming nothing can be found that meets the patient’s needs and fits into any of the above criteria, is a UK-manufactured special.

The last option, and one that should be avoided if at all possible, is an imported product that is unlicensed and not considered a medicine in the country of origin, for example, a food supplement from abroad with an ingredient that is regarded as a medicinal in the UK.
The MHRA states that the above hierarchy is for guidance only, and stresses the importance of considering every case on an individual basis.