Testosterone necessary for nocturnal erections, but waking erections depend on dopamine.

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From the group of studies below we can conclude:

  1. Nocturnal erections are testosterone-dependant (spinal reflexes), but wakeful erections are largely dopamine-dependant (brain).
  2. Supplementary testosterone given to men with low testosterone had little effect on daytime erections associated with watching porn.
  3. Erections from watching porn, or physical stimulation of the penis, involve a testosterone-independent system. In other words, they depend on the brain and reward circuitry dopamine.
  4. KEY POINT: One can have strong nocturnal erections (meaning one's testosterone is fine), yet have weak erections during the day when suffering from porn-induced ED (due to desensitization & sensitization)
  5. Experts assume that morning wood is simply a nocturnal erection, but many guys with porn-induced ED report no morning wood, and yet have nocturnal erections. I can't explain.

 The science of morning wood



Testosterone and sleep related erections an overview

J Sex Med. 2005 Nov;2(6):771-84.

Montorsi F, Oettel M.


Istituto Scientifico H. San Rafaele, Milan, Italy. Montorsi.francesco@hsr.it


Sleep-related erections have been reported to occur from the intrauterine life to senescence. It has been speculated that the main function of nocturnal erections is to provide adequate engorgement of the corpora cavernosa, which then leads to increased tissue oxygenation. This is in turn to prevent cavernous fibrosis, the histopathological basis for corporeal venoocclusive dysfunction, which probably is the most common cause of organic erectile dysfunction. It has been suggested that sleep-related erections are triggered by the release of nitric oxide by the nitrergic nerve fibers within the cavernous nerves. Androgens regulate this mechanism as well as some other non-nitrergic processes within the corpora cavernosa and within the central nervous system.

By contrast, the erectile response to tactile or visual erotic stimuli in wakefulness predominantly involves an androgen-independent system, although it may, at least to a certain degree, also be influenced by androgen-sensitive mechanisms. No doubt, androgens are key players in the physiology of nocturnal erections, and the availability of new, user-friendly testosterone preparations such as transdermal gel and intramuscularly administered testosterone undecanoate stimulates further investigations on this field. The prospect that the quality of sleep may also be improved by an androgen therapy administered to improve sleep-related erections in hypogonadal men needs further basic research and appropriate clinical studies.


The effects of testosterone replacement on nocturnal penile tumescence and rigidity and erectile response to visual erotic stimuli in hypogonadal men.

Psychoneuroendocrinology. 1995;20(7):743-53.

Carani C, Granata AR, Bancroft J, Marrama P.


Department of Endocrinology, Modena, Italy.


Nocturnal penile tumescence (NPT) and erectile response to visual erotic stimuli (VES) were measured, by means of a Rigiscan device, in nine hypogonadal men, and repeated after 3 months of androgen replacement. The same assessments were carried out once in 12 eugonadal controls. The number of satisfactory NPT responses, in terms of both circumference increase and rigidity, were less in the hypogonadal men than the controls and were significantly increased by androgen replacement, confirming the results of earlier studies. In terms of circumference increase, erectile response to VES did not differ between the hypogonadal men and the controls, and did not increase with androgen replacement. In terms of rigidity, the erectile response to VES did not differ between hypogonadal men and controls. However, in terms of both duration and maximum level of rigidity, there was a significant increase following androgen replacement in the hypogonadal men. These new findings, in relation to rigidity, require a modification of the earlier formulation, which saw NPT as androgen dependent and erectile response to VES as androgen independent. NPT, and possibly spontaneous erections at other times, clearly involve an androgen sensitive system. Erectile response to VES predominantly involves an androgen independent system but may also be influenced by androgen sensitive mechanisms.


Placing erection in context the reflexogenic psychogenic dichotomy reconsidered.

Neurosci Biobehav Rev. 1995 Summer;19(2):211-24.

Sachs BD.


Department of Psychology, University of Connecticut, Storrs 06269-1020, USA.


Penile erections are usually classified as arising from "reflexogenic" or "psychogenic" causes. In practice this dichotomy has translated, somewhat circularly, to a distinction between spinal vs. supraspinal mediation, pelvic vs. hypogastric neural mediation, and perineal somesthetic stimulation vs. stimulation of receptors innervated by the cranial nerves.

Evidence for differential regulation of erection in different contexts is reviewed. Research ascribing a physiological role to the hypogastric nerves in psychogenic erection, exemplified by classic studies of cats and spinally injured men, is suggestive but not compelling. Somewhat stronger is evidence that erection in some contexts (e.g., nocturnal penile tumescence (NPT) in humans or touch-stimulated erection in rats) is more sensitive to androgen levels than in other contexts (e.g., visual erotic stimuli in men or copulation in rats). However, some of these differences may arise from the relative erectogenic strength of the stimuli, rather than from qualitative differences in androgen sensitivity of different contexts. More compelling is the possibility that conflicting interpretations of the role of dopamine in erection may stem in large part from differences among laboratories in the context in which erection is evoked. In light of the evidence reviewed, it seems unlikely that the conventional reflexogenic-psychogenic dichotomy should be retained, at least in its present form. As a first step, it may be worth considering that reflexive erections may not be limited to somesthetic perineal stimulation, but rather may also include stimuli received via the cranial nerves. Two alternatives to the standard reflexogenic-psychogenic dichotomy are proposed. The first is a minor revision in which two senses of psychogenic erection are distinguished: the weak, commonly used, sense would include erection resulting from any extrinsic nonsomesthetic stimulation, whether visual, auditory, or chemosensory. In this sense, reflexive erections and psychogenic erections may not be mutually exclusive. The strong sense of psychogenic erection would be limited to memory and fantasy. The origins of psychogenic erection in both senses need not be available to consciousness, which may account for apparently spontaneous erections. In the second alternative taxonomy, erectogenic stimuli are classified as contact (somesthetic) or noncontact, and their action in evoking erection is placed on a continuum of reflexivity. Erectile contexts could then be considered as orthogonal to the other two dimensions. Even without a change in taxonomy, the conduct and interpretation of research into erectile function may be expected to benefit from closer attention to differences and similarities between contexts and species, and to context-sensitive differences in the regulation of erection.

One guy's advice:

Some people have it [morning wood], others don't. But it could mean you are low on testosterone, or are overtaxing your system like the others mention. And the later may cause the former.

I know that when I stopped PMO, my morning wood returned. Not to how it was when I was younger, but still pretty good. So if you want it back, stop the PMO. I know for me for some reason I felt a lot better when I woke up with it. More virile and alive and powerful.