Causes of Morning Erections in Men

Men often wake with an erection first thing in the morning, but did you ever wonder why?

A morning erection is scientifically known as a nocturnal penile tumescence (NPT). Informally, it's known as "morning wood." But it remains an enigma to men and women alike.

This article explores the phenomenon of morning erections, why they're associated with REM sleep, and other potential causes.

What Causes Morning Erections
Verywell / Brianna Gilmartin

The Role of REM Sleep

Morning erections correspond to the timing of rapid eye movement (REM) sleep. As part of normal sleep patterns, called sleep architecture, transitions occur throughout the night between the various sleep stages. People stay in REM stage sleep for longer as morning approaches. So by the time they wake, they are often coming out of REM sleep.

Specifically, REM sleep occurs 90 minutes after the onset of sleep. The first stage of REM usually lasts about 10 minutes, with each subsequent stage lengthening until the final stage lasts up to an hour. During a normal night of sleep, people usually experience about four or five stages of REM sleep. In all, REM sleep represents about 25% of total sleep time.

In addition to the vivid movie-like dreams that are characteristic of REM sleep, the penis also becomes erect and engorged with blood during these stages. This is due to the activity of the parasympathetic nervous system affecting the sacral nerve (actually, a group of five nerves in the lower back). When this occurs in the morning, the stiffened penis may be referred to in slang terms as "morning wood" or "morning glory."

Therefore, morning erections are secondary to the timing of REM sleep and the natural physiological processes that are associated with this sleep state in men. It seems that the body is doing what healthcare providers refer to as "testing systems" during sleep. This is a normal and healthy phenomenon in men. (And the response isn't unique to men; it's also possible for the clitoris of a woman to become engorged with blood and erect during REM sleep.)

Male erections typically go away within a few minutes after awakening. A persistent erection, where the blood fails to drain from an erect penis, may occur in a condition called priapism. On the other hand, a lack of morning erections may suggest a problem with the blood vessels or nerves or erectile dysfunction.

ED Is Very Common

 Erectile dysfunction—a condition in which a man is unable to get or keep an erection firm enough for satisfactory sexual intercourse—is very common among men. However, it is not a normal part of aging.

The Timing of "Sleep Erections"

Everybody has different sleep patterns, but since people usually experience about four or five stages of REM sleep during the night, many men have four or five erections during the night, too. Each erection can last 25 to 35 minutes (though not necessarily every night).

As noted, REM sleep becomes more prolonged towards morning. Although men do not always wake at the end of each episode of REM sleep, they are likely to awaken in the morning with an REM sleep-related erection. Erections are considered a normal part of sleep physiology in men.

The precise timing of these erections may be difficult to predict as there is quite a bit of variability. The length of time from the onset of the erection—with a 2 mm change in the circumference of the penis—to a full erection is usually 10 minutes.

The erectile function of the penis can be tested as part of a diagnostic sleep study called a polysomnogram. However, it is not a common procedure.

Other Potential Causes

Morning erections are easily traced to the last stage of REM sleep, but there are other potential, contributing causes, too. They include:

  • Levels of testosterone, which play a role in sexual function, are higher early in the morning compared to in the afternoon or evening.
  • The presence of prolactin, which stimulates several testicular functions in males. Its release is dependent on REM sleep. And its level spikes between 3 and 5 a.m., when REM sleep is dominant.
  • The workings of the autonomic nervous system. Penile erection is controlled by the autonomic nervous system. And several neurotransmitters, especially norepinephrine and acetylcholine, are regulators of penile erection that are fired during REM sleep. Simply put, the erections in REM sleep occur when neurological stimulators cause blood to flow to the penis.
  • Physical stimulation, which can occur even in a groggy, half-asleep, half-awake state. The body can remain alert to what's going on and respond with a morning erection.

Why Erections Should Be Reassuring

While you sleep, remember that your nervous system helps keep your body running. And the sacral nerve (part of the parasympathetic nervous system) is responsible for erections while you're asleep or half-asleep.

So from this vantage point alone, morning erections are a reassuring sign that your nerves, blood supply, and circulation are healthy. It can also mean you’re physically able to get and maintain an erection—either asleep or awake.

What If Morning Erections Stop?

If you do not wake with an erection, it is not necessarily abnormal. It could be that you did not wake from REM sleep. It is also possible that the erection began to fade prior to waking completely.

In general, sleep-related erections decrease with age. But if you're not waking at least occasionally with an erection, if may be time to visit your healthcare provider for a friendly check-up.

Try to keep in mind that you're a long way from worrying about a diagnosis of erectile dysfunction. Your provider will probably want to do a full health history and eliminate other possibilities (such as obstructive sleep apnea, which is just one condition that can affect erections).


Morning erections correspond to the timing of rapid eye movement (REM) sleep. During a normal night of sleep, people usually experience about four or five stages of REM sleep, and many men have four or five erections during the night. Although men do not always wake up at the end of each episode of REM sleep, they are likely to awaken in the morning with an REM sleep-related erection. Erections are considered a normal part of sleep physiology in men. Other causes may lead to morning erections, too, such as levels of testosterone, the presence of prolactin, the workings of the nervous system, and physical stimulation.

A Word From Verywell

You may be concerned that you're having too many or too few morning erections. Or maybe you've noticed a change in your morning "routine." If a physical matter is troubling you, you owe it to yourself and your peace of mind to make an appointment with your healthcare provider. In the meantime, remember the tenets of living a healthy lifestyle: Eat nutritious foods, keep your weight under control for your height and age, exercise regularly, drink minimal amounts of alcohol, and avoid cigarettes.

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6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Peever J, Fuller PM. The biology of REM sleep. Curr Biol. 2017;27(22):R1237-R1248. doi:10.1016/j.cub.2017.10.026.

  2. Youn, Gahyun. Why do healthy men experience morning erections? The Open Psychology Journal. 10. 49-54. doi:10.2174/1874350101710010049. 

  3. Anele UA, Morrison BF, Burnett AL. Molecular pathophysiology of priapism: Emerging targets. Curr Drug Targets. 2015;16(5):474-83. doi:10.2174/1389450115666141111111842.

  4. U.S. Department of Health and Human Services. National Institutes of Health. National Institute of Diabetes and Digestive and Kidney Diseases. Definition & facts for erectile dysfunction.

  5. Oakwood Health Network. Morning erection and erectile dysfunction.

  6. Men's Health. Why do you get morning wood? Believe it or not, there's an important scientific reason.