"The effectiveness of acupuncture for (seasonal allergies) compared with other antiallergic interventions and the possible underlying mechanisms of any effect, including context effects, need to be addressed in further research, " they write in the study.

CNN: Acupuncture may be antidote for allergies

The word antidepressant covers a wide range of medications that have very different mechanisms of action and very different side effect and risk profiles.

CNN: What are antidepressants' long-term effects?

Here, without the gravity effect, we can grow cells very purely and understand the mechanisms by which they are replicating.

WHITEHOUSE: President Obama's call to the International Space Station

Though the placebo effect remains largely shrouded in mystery, researchers attribute some aspects of the placebo response to active mechanisms in the brain that can influence bodily processes such as the immune response and release of hormones.

CNN: The power of perceptions: Imagining the reality you want