I found this information on the C Three Facebook page:

For those beginning TSM using nalmefene (Selincro), I would recommend you are in a comfortable and safe environment for the first time you take the tablet, preferably at home if possible. You are likely to have a few minor and temporary side effects which will go after a week or so but you cannot take half a nalmefene tablet in the same way you can naltrexone, so you are going from zero medication to a full dose the first time you take it. Have a small meal about 20 minutes before the tablet - toast is fine - it will help reduce any nausea.

It is NOT a good idea to take the tablet for the first time an hour before you are due to go out to a restaurant or bar and then be struck with panic if you start feeling disorientated and sick - that can be very frightening. Be kind to yourself and be aware that you are going to need a little time for your body to adjust to taking this medication. Once you are through the first 1 to 2 weeks, you should feel fine. If you have any questions about side effects, drop me an email on Joanna@cthreeeurope.com