Study: Marijuana makes you happy in low doses
A study found that marijuana in low doses is an anti-depressant, and in high doses is a depressant. The effect of medium doses was unknown.

[he’s a lil’ guy]
A new neurobiological study has found that a synthetic form of THC, the active ingredient in cannabis, is an effective anti-depressant at low doses. However, at higher doses, the effect reverses itself and can actually worsen depression and other psychiatric conditions like psychosis.
science daily