A safety review was carried out to evaluate the potential risk of Raynaud's phenomenon in patients taking Intuniv XR. Raynaud's phenomenon is a disorder of the blood vessels, mainly in the fingers and toes, where they episodically do not receive enough blood and oxygen. The resulting lack of blood and oxygen causes numbness and the skin will turn a pale or bluish colour. Most episodes of this phenomenon last about 15 minutes but in severe cases this can cause damage to the skin and muscle (through oxygen deprivation and tissue death). Health Canada started a review because other drugs used to treat ADHD contain warnings in their product safety information about the risk of Raynaud's phenomenon. The review aimed to determine whether there was enough evidence to include a similar stronger warning for Intuniv XR.