This is rubbish. If someone wants the drug that much - buy it yourself!
It is a lifestyle choice.
If you do X you might get aids. Answer. Don't do X.
What if there was a £400 per month anti skin cancer drug that would let me go on sunbeds or out in the sun without suncream. Would the NHS fund me for that. No. They would say wear suncream!
If I only ever eat crisps or chocolate because it doesn't suit my lifestyle to cook healthy food, will the NHS pay for me a personal chef for £400 per month as a preventitive measure to me having a heart attack or diabetes?