Sonnet 76 is being presented as evidence, but there are certainly allusions to drug use and warped perception in
A Midsummer Night's Dream. It's so obvious as to be unavoidable.
Shakespeare was a very, very formulaic writer, so sonnet 76 is him basically answering criticism that he does the same old thing all the time (and I don't really know how much he was criticized for that, though). He basically says that his style and staid formula is timeless like the Sun, which is timeless like the love he has for the lady he is addressing the sonnet to. (There were others like George Herbert who were doing all kinds of inventive things - making the text of his poems into the shape of what he was writing about, for e.g., like an altar or even a butterfly, I think).
"Compounds strange" may refer to stylistic choices as well as drugs, "noted weed" may refer again to something very familiar, which has become stale and unattractive.
Anyway, pot head? Ehh. Did he try some drugs? Oh, I bet.
