I absolutely think the single convention is being used as camouflage, with the drug warriors saying, "I would love to deschedule cannabis, but my hands are bound". Having said that, any treaty can be amended but it ain't easy, which is one very significant reason to avoid treaties in the first fucking place.
Is the USA bound by it? The simple answer is yes, treaties have the full force of the constitution behind them, which is, again, a very good reason to avoid (complicated) treaties in the first place.
I have no objection to entering into a treaty that fully comports with the US constitution, but I am quite leery of a treaty that does not afford citizens of other countries the right to keep and bear arms, for example. It's fine for other countries to have such overbearing laws but there is no need for us to enter into such a treaty.
From a philosophical, American point of view, why would our leaders enter into a treaty that contradicts the US constitution on such a fundamental right? Is it because our leaders fundamentally dishonor the US constitution, yes I am thinking of Obama and Hillary when I say this? Do we want leaders like that? Do we, as a people, believe that other people should not be free?
Just to be clear, I am not arguing that the US constitution should be applied anywhere except for the US. I fully respect the UK's decision to be a nanny state, but I see no reason for the US to join in such foolishness.