Chris Jones, the chief executive of the MS Trust, said it was "frustrating" that there was no clear physical proof that cannabinoids helped relieve spasticity.

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The anti-spasticity medication (brand names Kemstro and Lioresal) was earlier touted as an antidote for cocaine abusers in a study by the UCLA Neuropsychiatric Institute.

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In a statement, NHS North Yorkshire and York said it did not "routinely fund the prescribing of Sativex for patients with multiple sclerosis symptoms including spasticity and pain".

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Studying these creatures, Dr Zoghbi saw that the rodents with a mutant form of the gene were affected similarly to people: they developed tremors and spasticity in their forelimbs, became susceptible to seizures and suffered breathing problems.

ECONOMIST: Neuroscience (1)