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Nocturnal Penile Tumescence

During REM sleep, the brain produces smaller amounts of certain neurotransmitters. One is norepinephrine, which plays a role in erections. Norepinephrine’s job is to stop blood from flowing to the penis to prevent erections at inappropriate times.

But during REM sleep, levels of norepinephrine decrease, allowing testosterone to trigger more blood flow to the penis and, consequently, an erection. This cycle might occur four or five times a night.

Men often wake up with erections because they are just finishing a phase of REM sleep.

Some men might feel a little embarrassed by NPT, but these erections are natural and normal. They help keep the penis in working order. In fact, men who don’t have NPT should see their doctor to make sure everything is all right.

Print this article or view it as a PDF file here: Nocturnal Penile Tumescence


ASAP Science

“The Science of ‘Morning Wood’”

(Video. November 14, 2012)

International Society for Sexual Medicine

“What is nocturnal penile tumescence (NPT)?”

Medical Daily

Borreli, Lizette

“The Science Of Morning Wood: Electrical Impulses In Brain Increase Blood Flow To Penis In REM Sleep”

(October 16, 2014)

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