From what I read this will be perscribed using the Sinclair Method Approach

Error

To be released in certain markets in the EU in mid 2013.

Nalmefene

17-cyclopropylmethyl-4,5α-epoxy-6-methylenemorphinan-3,14-diol

Naltrexone

17-(cyclopropylmethyl)-4,5α-epoxy- 3,14-dihydroxymorphinan-6-one

They look the same in form from the image in wikipedia except they are made of different substances. Nalmefene is not metabolised by the liver like naltrexone is.

I dont know on how it differs to Naltrexone apart from that - Maybe others here know.