one hypothesized mechanism by which antidepressant medications to regulate mood is the suppression of sleep.

One hypothesized is the suppression of REM sleep.
Sleep is categorized into different stages and one of these stages is the REM sleep. REM sleep usually occur after about one and half hours after sleeping.
Although sleep deprivation has been associated with some negative effects, the effects that result from deprivation of REM sleep seem to be less profound. Some research study has even reported that, deprivation of REM sleep has beneficial effects on people suffering from major depression and many antidepressant drugs have their mechanism of action based on this fact.

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