I want to know, if when taking Naltrexone one cannot have pain killers like Morphine, then what is the alternative? I always think if I had strong pain and was in hospital what would they use that does not operate on the opioid receptors?

Yes because it blocks opiod receptors morphine, tramadol, codeine will not have the same effect. Boxes of Nal usually come with warning cards you can pop into your wallet, these cards alert medical staff to the fact you may have consumed Nal and explain the protocol they need to follow when administering pain relief. If you knew in advance you'd be requiring morphine I'd simply not take any nal for a few days.

I posted this in another thread but its worth posting twice.

Make sure your system is clear of opiates before taking Nal as it will send you into opiate withdrawal. I was using Codeine last year and only waited a couple of days before starting Nal again. After an hour I though I was going to die.