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What Is Morning Wood? Why It Happens and What It Says About Sleep and Health

Morning wood is a sleep phenomenon first. Here is what the research says about why it happens.

Men's Health Weekly staff · October 25, 2026

The quick answer

Morning wood is nocturnal penile tumescence, erections during sleep that occur predominantly in REM sleep, per a 2026 review.¹
Testosterone rises during sleep, peaking at the start of REM, but in 67 healthy men aged 45 to 74 its link to nocturnal erections faded after adjusting for age.²³
In 3,888 men seeking ED care, 63.6% reported reduced sleep-related erections, and a greater reduction tracked with lower testosterone and higher cardiovascular risk.⁴
We found no study that sets a normal number of mornings per week.

Morning wood is the everyday name for nocturnal penile tumescence: erections that happen during sleep and are often still present on waking. They happen mostly during rapid eye movement (REM) sleep and are a normal part of male erectile physiology.¹⁵ Below is what is known about why they happen, how they change with age, and what the evidence does not say.

Why does morning wood happen?

Erection is a nerve and blood-flow process, and it is switched on and off during the night. A 2026 review in the International Journal of Impotence Research describes sleep-related erections as occurring predominantly during REM sleep, and proposes that they help keep penile tissue oxygenated.¹ Because REM periods get longer toward morning, the last one of the night is often the one a man wakes in, which is why the erection tends to be noticed then.¹

Popular explanations include a full bladder. We found no study in the sources reviewed this run that tests that idea, so we do not state it as a cause.

Does testosterone play a part?

It appears to contribute, but the link is not simple. Testosterone rises during sleep, with peak levels coinciding with the start of REM.² In a sleep-laboratory study of 67 healthy men aged 45 to 74, bioavailable testosterone correlated with several measures of nocturnal erections, but the link disappeared once age was accounted for, and it was only clear in the 55 to 64 age group.³ In plain terms, testosterone is one input among several.

How does morning wood change with age?

Sleep-related erections tend to become less frequent as men age, and the same 2026 review says ageing both reduces them and increases sleep disturbances.¹ We found no study that gives a normal number of mornings per week, and any figure quoted without a source should be treated with care. If the question is the opposite one, the pattern of missing erections and what it can signal, see what not getting morning wood can mean.

What can reduce morning erections?

Factor	What the sources say
Disrupted or short sleep	Fragmented REM sleep, sleep apnea and sleep deprivation are linked with fewer sleep-related erections in the 2026 review.¹
Low testosterone	In men with ED, more severe reduction in sleep erections tracked with lower testosterone.⁴
Blood vessel and metabolic disease	The same clinic study tied fewer sleep erections to higher glucose, triglycerides and cardiovascular risk.⁴
Depression, smoking, aging	These can influence overnight erection recordings.⁶
Medicines, alcohol, inactivity	The NIDDK lists some medicines, heavy drinking and low activity among causes of ED.⁷

Is morning wood a sign of health?

It is one clue, not a test. Reduced sleep-related erections are common in men seeking help for ED: 63.6% of 3,888 men at an Italian clinic reported them, and the men with more severe reduction were more likely to have metabolic and vascular risk factors.⁴ That study looked at men who already had erection complaints, so it cannot say how worried a man with normal erections should be. Overnight monitoring has been used to help sort psychological from physical causes of ED, but it has limits and is not a home test.⁶

When should a man ask a doctor?

Sleep-time erections have clearly dropped off for weeks or months.
Erections while awake are also harder to get or keep. See which doctor to see for ED.
The change came with low mood, low desire, heavy snoring, poor sleep or a new medicine. See how ED and low testosterone are connected.

One missing morning is not a diagnosis. The pattern over weeks matters more than any single day.

Bottom line

Morning wood is a normal, mostly REM-driven part of male physiology that typically thins out with age. It reflects sleep, hormones and blood flow together, and a lasting change is worth discussing with a clinician.

Talk to a clinician. This article explains the evidence; it cannot tell you what is right for you. A licensed clinician who knows your health history and medications can.

Important safety information. PDE5 inhibitors (sildenafil, tadalafil, vardenafil) must not be taken with nitrates in any form, including nitroglycerin, or with guanylate cyclase stimulators such as riociguat, and need caution with alpha-blockers.⁸ The most common side effects are headache and flushing.⁸ An erection lasting more than four hours needs emergency care, and sudden loss of vision or hearing means stopping and getting medical help right away.⁹ Only a licensed clinician who knows your health history and medications should decide whether these are safe for you.

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