The
medical trade, which is what he said, can mean a lot of things. It can mean the people who sell the stuff online, and by and large (there is no standard) it would often appear to be 100mg as that is probably the most sold dosage, partly as it is the most cost-effective.
What the medical
establishment recommend is sometimes different. Anyone can check that under the BNF (British National Formulary) which is the reference book your doctor uses (though is not
obliged to follow). The BNF states:
ADULT over 18 years initially 50 mg approx. 1 hour before sexual activity, subsequent doses adjusted according to response to 25–100 mg as a single dose as needed; max. 1 dose in 24 hours (max. single dose 100 mg)
HOWEVER there is a reason for this. Good Medical Practice (which you can reference from the BMA or any good medical handbook) requires doctors always (as a general
rule) to commence treatment with the least invasive treatment that may work. The lowest highly effective dose statistically for sildenafil (which you can confirm by looking up the various studies) is 50mg. So your GP is
generally advised to begin treatment at that dose and wait for patient feedback and vary the dose as required. My opinion is that a lot of doctors may simply prescribe 100mg though, especially in an older patient. This is possibly an instinctive balance between costs and likely effectiveness. (You can look up sildenafil in the England prescribing statistics and while some statistics include differences in dose, a lot don't.) Although the NHS claim that prescribing is not based on cost, my own analysis shows that some medicines are miraculously considered better or worse depending on the sudden price changes!