In the double-blind, randomized control trial, half the women got tenofovir gel and half got a placebo.

CNN: Gel cuts HIV transmission rate in study

And in a study published last year, researchers in Australia showed in a double-blind, placebo-controlled trial that subjects with suspected gluten sensitivity had substantially fewer symptoms on a gluten-free diet than control subjects who unknowingly ingested gluten.

WSJ: New Guide to Who Really Shouldn't Eat Gluten