Colour me dim (I suspect I actually knew this, but had forgotten), but I went for my screen at Praed St today, and the nurse mentioned that clotrimazole pessaries (Canesten or generic) can weaken latex condoms - for up to seven days after use. I don't think I'd ever really noted this before. So if you self-medicate for thrush with the pessaries or cream, switch to non-latex condoms for a few days to be on the safe side.