The post-orgasmic prolactin increase following intercourse is greater than following masturbation and suggests greater satiety

Abstract

Research indicates that prolactin increases following orgasm are involved in a feedback loop that serves to decrease arousal through inhibitory central dopaminergic and probably peripheral processes. The magnitude of post-orgasmic prolactin increase is thus a neurohormonal index of sexual satiety. Using data from three studies of men and women engaging in masturbation or penile-vaginal intercourse to orgasm in the laboratory, we report that for both sexes (adjusted for prolactin changes in a non-sexual control condition), the magnitude of prolactin increase following intercourse is 400% greater than that following masturbation. The results are interpreted as an indication of intercourse being more physiologically satisfying than masturbation, and discussed in light of prior research reporting greater physiological and psychological benefits associated with coitus than with any other sexual activities.

Full text

The post-orgasmic prolactin increase following intercourse is
greater than following masturbation and suggests greater satiety
Stuart Brody
a,
*
, Tillmann H.C. Kru
¨
ger
b
a
Division of Psychology, School of Social Sciences, University of Paisley, Scotland, UK
b
Institute of Behavioral Sciences, Psychology and Behavioral Immunobiology, Swiss Federal Institute of Technology, Zu
¨
rich, Switzerland
Received 20 May 2005; accepted 21 June 2005
Available online 10 August 2005
Abstract
Research indicates that prolactin increases following orgasm are involved in a feedback loop that serves to decrease arousal through
inhibitory central dopaminergic and probably peripheral processes. The magnitude of post-orgasmic prolactin increase is thus a
neurohormonal index of sexual satiety. Using data from three studies of men and women engaging in masturbation or penile–vaginal
intercourse to orgasm in the laboratory, we report that for both sexes (adjusted for prolactin changes in a non-sexual control condition), the
magnitude of prolactin increase following intercourse is 400% greater than that following masturbation. The results are interpreted as an
indication of intercourse being more physiologically satisfying than masturbation, and discussed in light of prior research reporting greater
physiological and psychological benefits associated with coitus than with any other sexual activities.
# 2005 Elsevier B.V. All rights reserved.
Keywords: Prolactin; Sexual behavior; Trials; Intercourse; Masturbation
1. Introduction
In addition to its role in lactogenesis, plasma prolactin has
other functions, including reflecting inversely central
dopaminergic activity. The postorgasmic rise in prolactin
appears to reflect sexual satiety produced by a negative
feedback loop: the more sexually satiated one is following
sex, the greater the relief, and the greater the drop in sexual
tension and desire (Kru
¨
ger et al., 2002). This prolactin effect
is specific to orgasm, and does not occur following non-
orgasmic sexual arousal (Kru
¨
ger et al., 2003). The post-
orgasmic plasma prolactin increase appears to offset the
central dopamine effects during arousal and orgasm, and
also may have peripheral inhibitory effects (Kru
¨
ger et al.,
2002). In addition to the phasic effects of brief prolactin
increases, there are sexual inhibitory effects of baseline
prolactin levels: in a group of older men, unstimulated serum
prolactin levels were strongly inversely (r = 0.75) related
to the men’s frequency of sexual intercourse (Weizman
et al., 1983).
A growing research literature has demonstrated that
penile–vaginal intercourse differs from other sexual
behaviors in many ways, including associations with indices
of better physical and psychological function in both sexes.
For example, in healthy young adults, frequency of
intercourse but not of other sexual activities is associated
with better cardiovascular autonomic function (Brody, 2006;
Brody and Preut, 2003) and with slimness (Brody, 2004). In
a clinical trial, high-dose ascorbic acid supplementation
(ascorbic acid potentiates dopamine’s inhibitory effect on
prolactin release) increased intercourse but not other sexual
behavior frequency (Brody, 2002). For women, frequency of
intercourse (but not of other sexual activities) is associated
with greater ability to identify their emotions (Brody, 2003),
and their consistency of orgasm during intercourse (but not
during other sexual activities) is associated with better
concordance of subjective and genital indices of sexual
arousal (Brody et al., 2003). There was less vaginal atrophy
in postmenopausal women having penile–vaginal inter-
course at least thrice monthly than in those having
www.elsevier.com/locate/biopsycho
Biological Psychology 71 (2006) 312–315
* Corresponding author. Fax (USA): +1 561 431 3114.
E-mail address: stuartbrody@hotmail.com (S. Brody).
0301-0511/$ – see front matter # 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.biopsycho.2005.06.008

intercourse less than 10 times annually; in contrast,
masturbation showed no protective effect (Leiblum et al.,
1983). Studies have also found that women’s frequency of
masturbation (but not intercourse) was associated with past
or present depression (Cyranowski et al., 2004; Frohlich and
Meston, 2002), and also found that depressed women
reported a more intense desire for masturbation, less sexual
pleasure and less sexual satisfaction than did nondepressed
women (Frohlich and Meston, 2002).
The present report uses data from three prior studies of
the prolactin responses of men and women to coitus or
masturbation (and to the respective control conditions)
(Exton et al., 1999, 2001; Kru
¨
ger et al., 1998) to examine the
prolactin response as a function of specific sexual activity.
Those three reports did not compare differences between
sexual behaviors. Because the post-orgasmic prolactin
response is an objective physiological index of sexual
satiety, the post-orgasmic prolactin response can be used to
compare the effects of orgasm from coitus to the effects of
orgasm from other sexual behaviors. Given the previous
findings of intercourse but not other sexual behaviors being
associated with better psychological and physiologic
function (Brody, 2003, 2004, 2006; Brody and Preut,
2003; Brody et al., 2003, 2000; Cyranowski et al., 2004;
Frohlich and Meston, 2002; Leiblum et al., 1983), it was
hypothesized that intercourse would produce a greater post-
orgasmic prolactin increase than would masturbation,
reflecting greater physiological satiety.
2. Methods
2.1. Participants
Participants were recruited via an advertisement at the
Hannover Medical School. Participants passed a general
medical examination, which included the exclusion criteria
of medication use (other than oral contraception), over-
weight, suspicion of drug or alcohol abuse, or any indication
of sexual dysfunction or of endocrine or psychological
disorders. All participants were clearly comfortable with the
idea of sexual activity in the laboratory. Only exclusively
heterosexual persons participated. After a complete descrip-
tion of the procedures, written informed consent was
obtained. Participants were asked to refrain from any sexual
activity, alcohol, or drug use for at least 24 h before
laboratory sessions. Women were examined during the
early- to mid-follicular phase of their menstrual cycle. There
were no dropouts. Data from all subjects from the three
studies was included. Complete data was available for 19
men and 19 women (nine men and 10 women in the
intercourse group, 10 men and nine women in the
masturbation group). The mean ages of the subjects did
not differ between studies (M = 26.2). About 75% of the
participants were students at the Hannover Medical School,
and the remainder were other graduate students. Further
details are available elsewhere (Exton et al., 1999, 2001;
Kru
¨
ger et al., 1998). All studies were conducted at the
Hannover Medical School. The studies were approved by the
Hannover Medical School Ethics Committee and conducted
in accordance with the Declaration of Helsinki.
2.2. Materials and procedure
The masturbation condition involved masturbation in
private while watching an erotic film. The control condition
involved no sexual activity, and the viewing of a nonsexual
documentary film. In both conditions, physical activity was
the minimum required for the task.
The penile–vaginal intercourse condition involved view-
ing an erotic film together, followed by the measured partner
lying passively supine on a bed, with their partner active on
top of them until the measured partner had an intercourse
orgasm. The control condition involved silently watching a
nonsexual documentary film with their partner (without
physical contact). In both conditions, physical activity on the
part of the measured subject was the minimum required for
the task (thus, comparable to the masturbation studies).
Orgasm was determined by the presence of all three of the
following indicators: (1) self-report immediately after
orgasm (via an intercom), (2) self-report confirmation at
the end of the laboratory session, and (3) the detection of the
characteristic post-orgasmic rise in prolactin (Kru
¨
ger et al.,
2003). Subjective orgasm ratings and other hormonal assays
were available for the masturbation but not for the coital
sessions, thereby precluding any comparisons of those other
variables.
An intravenous cannula was inserted into a brachial vein
30 min before the start of each session. After the session
began, blood was collected using a pump from the other end
of the tube (in another room) at 1 ml/min every 10 min for
60 min. For the purpose of this analysis, only the changes
from the second baseline to the last post-orgasmic
measurement (and the analogous control condition times
to be used as a covariate as described below) were examined.
Blood was collected into EDTA tubes, centrifuged at 4 8C,
and stored at 70 8C until assayed (in a laboratory of the
Department of Endocrinology, Hannover Medical School)
with a commercially available immunoradiometric kit
(Prolactin-MAIAclone, Biodata S.p.A., Rome, Italy). The
inter- and intra-assay variation was substantially below 10%
in all cases. Further details are available elsewhere (Exton
et al., 1999, 2001; Kru
¨
ger et al., 1998).
2.3. Design
To allow comparisons between studies, as well as to
control for individual responses to the control condition, a
two-way analysis of variance (ANOVA) was used. The
dependent variable was the final post-orgasmic prolactin
value minus the second baseline value; the independent
variables were sexual activity (intercourse versus
S. Brody, T.H.C. Kru
¨
ger / Biological Psychology 71 (2006) 312–315 313

masturbation) and biological sex; and the covariate was the
final prolactin control value (comparable in timing to the
final post-orgasmic value) minus the second control
baseline value.
3. Results
There was a significant main effect of type of sexual
activity (F(1, 33) = 5.0, p < .05), but no main (F(1, 33) < 0.1,
p > .95) or interaction (F(1, 33) < 0.1, p > .95) effects of
sex differences. The post-orgasmic prolactin changes from
baseline (adjusted for response to the control conditions) were
(ng/ml): male intercourse M = 15.62, S.E. = 6.33; male
masturbation M = 3.05, S.E. = 5.36; female intercourse
M = 15.71, S.E. = 5.55; female masturbation M = 3.06,
S.E. = 5.87.
Table 1 presents the course of prolactin levels as a
function of condition (sexual or control), type of sexual
activity, time, and biological sex.
S. Brody, T.H.C. Kru
¨
ger / Biological Psychology 71 (2006) 312–315314
Table 1
Course of prolactin levels as a function of condition, sexual activity, time, and biological sex
Biological sex Sexual activity Time (min) Condition Prolactin M (ng/ml) Prolactin S.E. (ng/ml)
Male Intercourse 10 Sexual 7.141 2.274
Control 6.989 0.641
20 Sexual 6.458 2.386
Control 6.833 0.636
30 Sexual 7.093 2.434
Control 6.233 0.681
40 Sexual 9.130 3.255
Control 5.867 0.709
50 Sexual 11.616 7.216
Control 5.544 0.698
60 Sexual 11.323 7.105
Control 5.267 0.698
Masturbation 10 Sexual 5.370 2.157
Control 5.590 0.609
20 Sexual 5.080 2.264
Control 5.220 0.603
30 Sexual 5.220 2.310
Control 5.160 0.646
40 Sexual 6.340 3.088
Control 4.930 0.672
50 Sexual 7.410 6.846
Control 4.760 0.662
60 Sexual 6.860 6.740
Control 4.650 0.662
Female Intercourse 10 Sexual 14.717 2.157
Control 7.530 0.609
20 Sexual 16.007 2.264
Control 7.870 0.603
30 Sexual 16.501 2.310
Control 8.030 0.646
40 Sexual 22.001 3.088
Control 8.090 0.672
50 Sexual 36.752 6.846
Control 7.910 0.662
60 Sexual 37.211 6.740
Control 8.010 0.662
Masturbation 10 Sexual 9.811 2.274
Control 7.678 0.641
20 Sexual 9.767 2.386
Control 7.978 0.636
30 Sexual 10.067 2.434
Control 8.167 0.681
40 Sexual 13.244 3.255
Control 8.267 0.709
50 Sexual 18.389 7.216
Control 8.111 0.698
60 Sexual 18.889 7.105
Control 8.178 0.698

4. Discussion
For both sexes, penile–vaginal intercourse produced a
substantially greater (adjusted for response to control
conditions, the increase was about five times as great)
post-orgasmic prolactin increase than did masturbation. The
characteristic post-orgasmic prolactin increase reflects
sexual satiety produced by a negative feedback loop (Kru
¨
ger
et al., 2002, 2003). The results imply that for both men and
women, there is a neuroendocrine indication of greater
satiation following an intercourse orgasm than following a
masturbation orgasm.
It is interesting to consider these results in light of the
finding that women who are orgasmic by both intercourse
and by other means report that intercourse orgasms are more
satisfying (Davidson and Darling, 1989). The results are also
consistent with evolutionary pressures, in which the one
potentially reproductive sexual activity would be expected
to be more physiologically rewarding than other sexual
activities.
The results are also consistent with the growing literature
on penile–vaginal intercourse differing from other sexual
behaviors, notably with regard to intercourse being
associated with indices of better physical and psychological
function (Brody, 2002, 2003, 2004, 2006; Brody and Preut,
2003; Brody et al., 2003, 2000; Cyranowski et al., 2004;
Frohlich and Meston, 2002; Leiblum et al., 1983). The
results raise the possibility that at least part of the means by
which intercourse becomes associated with better physical
and psychological function involves the mechanism of
intercourse orgasm resulting in greater phasic peripheral
prolactin increases. These greater phasic peripheral pro-
lactin increases likely reflect some combination of coitus
producing (relative to other sexual activity): (1) greater
physiological sexual excitation provoking a greater homeo-
static countervailing force (for example, greater central
nervous system dopaminergic activity would be offset by
greater prolactin increases (Kru
¨
ger et al., 2002)) and (2)
more complete orgasmic release and satiety. Better
regulation of central neurotransmission might be expected
to result in better psychophysiological function. Thus, the
far greater prolactin response caused by penile–vaginal
intercourse orgasm (compared to that caused by masturba-
tion orgasm) implies one psychobiological mechanism for
the multiple findings of intercourse but not other sexual
behaviors being associated with better psychological and
physiological function (Brody, 2002, 2003, 2004, 2006;
Brody and Preut, 2003; Brody et al., 2003, 2000;
Cyranowski et al., 2004; Frohlich and Meston, 2002;
Leiblum et al., 1983).
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