ORIGINAL ARTICLE Recreational use of erectile dysfunction medication may decrease confidence in ability to gain and hold erections in young males

(2007) 19, 591 596 & 2007 Nature Publishing Group All rights reserved 0955-9930/07 $30.00 www.nature.com/ijir ORIGINAL ARTICLE Recreational use of erectile dysfunction medication may decrease confidence in ability to gain and hold erections in young males P Santtila, NK Sandnabba, P Jern, M Varjonen, K Witting and B von der Pahlen Department of Psychology, Center of Excellence in Behavior Genetics, Åbo Akademi University, Turku, Finland We aimed to estimate the frequency of recreational use of erectile dysfunction medication (EDM) and to identify any adverse effects on confidence in gaining and holding erections resulting from such use. In addition, we explored differences in erectile function and sexual behavior between recreational and medicinal users of EDM to control for the possibility of recreational users having but not admitting erectile dysfunction. A subset from the Genetics of Sex and Aggression population-based sample of 4428 males with a mean age of 29.51 (s.d. ¼ 6.77) years provided information on their use of EDM, erectile function during first intercourse and currently, sexual behavior and confidence in their ability to gain and hold erections. There were 2.6% (n ¼ 115) recreational and 0.9% (n ¼ 39) medicinal users of EDM. Recreational users had currently significantly lower confidence in their erectile ability than non-users even though they had significantly better erectile function and significantly more unrestricted sexual behavior as well as had more confidence when initiating sexual activity. More frequent use of EDM was associated with significantly less confidence in erectile ability among the recreational users. We conclude that recreational users of EDM may be vulnerable for becoming psychologically dependent on pharmacologically induced erection. (2007) 19, 591 596; doi:10.1038/sj.ijir.3901584; published online 26 July 2007 Keywords: iatrogenic sexual dysfunction; erectile dysfunction; erectile dysfunction medication; sildenafil; confidence in erectile ability; recreational use Introduction Erectile dysfunction (ED) is one of the most common sexual dysfunctions in males. 1 A review article of 67 studies on ED concluded that 5 20% of men suffer from moderate to severe ED, with figures ranging from 5 to 35% in different studies. 2 For mild to moderate ED, prevalence rates range up to around 50%. Although a number of treatment options are available, men prefer oral erectile dysfunction medications (EDMs). 3 In empirical studies, sildanefil (Viagra), taldalafil (Cialis) and vardenafil (Levitra) have all shown to be effective for treatment of organic, mixed and psychogenic ED. 4 All of these also require sexual stimulation to work effectively and their effect is dependent on the mood of the Correspondence: Dr P Santtila, Department of Psychology, Center of Excellence in Behavior Genetics, Åbo Akademi University, Turku 20500, Finland. E-mail: pekka.santtila@abo.fi Received 26 April 2007; revised 29 May 2007; accepted 3 June 2007; published online 26 July 2007 man. 5 The relative high placebo effects reported suggest that EDM partly works by reducing men s performance anxiety. 6,7 Although intended for treatment of ED, EDM can be used recreationally 8 to enhance sexual performance even though no population-based studies of the prevalence of recreational as opposed to medicinal use of EDM have been conducted so far. A survey of 234 sexually active men between the ages of 18 and 25 found that 13% of the participants reported ED. 9 Six percent of all participants used EDM. About 60% reported using EDM to treat ED whereas about 30% reported using it in order to have more sex. Only 7.7% of those using EDM had obtained it from a physician. Also, of men attending a clinic for sexually transmitted diseases in San Francisco, about 17% reported using EDM in the past year. 10 Gay or bisexual men were significantly more likely to use EDM and among them over half received the drug from a friend (56%) rather than a health-care provider (42%). EDM users had a higher number of sex partners compared with non-users. Similar results have been reported also in a UK sample. 11 Further, an interview study of night club

592 customers reported that 3% of the participants reported using EDM as a recreational drug. 8 A third of these users were women. All said they would take EDM again. According to information from Finnish Customs (www.tulli.fi), EDM was involved in 300 out of the 703 confiscations of illegally imported medicines during 2005. Even though these results seem to suggest that at least some of the participants were using EDM for recreational purposes and not to treat ED, the possibility remains that they were actually suffering from ED but did not want to acknowledge that. It is well known that sexual dysfunctions are associated with reluctance to acknowledge them with only 25% of men with ED consulting a medical professional. 12 Recreational users, if not really suffering from ED, could be expected to show less ED before the onset of EDM use as well as currently compared to medicinal users. Also, they could be expected to be more unrestricted in their sexual behavior (more sexual partners overall, more expected sexual partners and more one-night stands ) and, if using EDM to prolong their erections, to report having more than one ejaculation during a single sexual encounter. Reports regarding adverse effects associated with recreational EDM use have been limited to its role in making the users more likely to engage in unsafe sex, especially when the EDM is used in association with illegal drugs. 10,11 Less attention has been given to the potential role of EDM usage in leading to adverse psychological effects. Confidence in one s ability to gain and hold an erection has been identified as a major psychological factor in ED. The confidence item of the International Index of Erectile Function (IIEF) 13 has been shown to be the second most important variable differentiating between men with and without ED preceded only by the item concerning the ability of the men to maintain erections until the end of the intercourse. 14 Men may believe that erections should be gained automatically whenever an opportunity for sexual activity arises and that the erections should continue until orgasm. 15 With such expectations, occasional difficulties with getting and keeping erections may create performance anxiety that then generates ED. 5 EDM use alleviates such performance anxiety. However, it may lead to decrease in the confidence of users in gaining and holding erections without the medication. Also, as EDM has been reported to enhance the rigidity of erections and prolong them, 16 it may be that recreational use changes the standards for acceptable erection in the minds of the users, thereby making them less content with nonpharmacologically induced erections. We aimed, first, to estimate the frequency of both medicinal and recreational use of EDM in a population-based sample of Finnish men. Second, we wanted to clarify whether the two groups of EDM users differed from each other and from non-users. We expected recreational users to have experienced less ED during their first intercourse compared to medicinal users and not to differ from non-users. We also expected them to show better current erectile function, to be more unrestricted in their sexual behavior and to be more likely to experience more than one ejaculation in a single sexual encounter. Third, we explored the effects of recreational EDM use on confidence in ability to gain and hold erections. We expected recreational users to show overall less confidence compared to non-users. We also expected more frequent use of EDM to be associated with less confidence in the group of recreational users. Method Participants The analyses presented in the present study were based on 4428 male twins and their siblings who had provided information on their use of erection medication. The mean age of the males was 29.51 (s.d. ¼ 6.77) years. The participants consisted of 3492 twins and 936 of their male siblings. Of the participants, 70.9% had a regular sexual partner and 8.5% reported having engaged in sexual behavior with a member of the same sex at some point in their lives. Participants were a subset from the Genetics of Sex and Aggression (GSA) Sample. The main GSA sample consists of two different data collections. The first data collection was carried out in 2005 and targeted 33- to 43-year-old twins. Twin pairs were sampled beginning from 33-year-old twins and progressing toward older twins until a final sample of 5000 twin pairs (10 000 individuals) had been identified. Questionnaires followed by a reminder letter and later a new questionnaire were sent to these individuals and finally returned by 3604 both male and female respondents resulting in an overall response rate of 36%. The response rate was lower for male (27%) when compared to female (45%) respondents. The second data collection was carried out in 2006 and targeted 18- to 33-year-old (there was no overlap between the data collections) twins and their over 18-year-old siblings. A total of 23 577 individuals were contacted by postal mail and asked if they would be interested in completing a questionnaire and to give saliva samples for DNA and hormone analyses (as the present study does not report on the DNA and hormone samples, no further information is given regarding them). Participants who consented to participate were given the option of completing the questionnaire by postal mail or online, through a secure webpage. Those who did not want to receive the questionnaire were instructed to notify the researchers of that by either returning the inquiry of interest in a pre-paid

envelope or through the webpage. Next, the questionnaire was sent followed by a reminder letter. A separate simultaneous longitudinal twin study was being conducted including some of the targeted individuals. Therefore, the reminder letters were only sent to individuals unique for the present study. Finally, a total of 10 524 both male and female participants responded to the survey, yielding an overall response rate of 45%. The response rate was lower for male (34%) than for female (56%) respondents. It should be noted that the response rates for both data collections represent underestimates due to changing addresses. According to Statistics Finland (www.stat.fi) approximately 15% of Finns move each year. Considering that the data collections lasted in each instance for over half a year, the real response rate was approximately 40% for the first and 50% for the second data collection. In all, a total of 4645 males returned the questionnaire. There were no differences between those providing information on their EDM use and those not doing so in terms of ED or confidence in erection. For both data collections, the participants addresses were obtained from the Finnish population registry. In the materials sent to the participants, the purpose of the study was described closely and the voluntary and anonymous nature of the participation was explained. The research plan for the first data collection consisting only of a questionnaire study was approved by the Ethics Committee of the Department of Psychology at Åbo Akademi University and for the second data collection also including DNA and hormone samples by the newly set up Ethics Committee of the Åbo Akademi University. Instruments Erectile dysfunction medication use. The participants first indicated if they have used an oral EDM (such as Viagra or Cialis) during the previous 4 weeks. If they responded yes, they were asked to explain whether it was to treat an ED diagnosed by a physician or for recreational reasons. The participants were also asked to indicate in how many of their intercourses during the previous 4 weeks they had been using erection medication. The response options were had not had sex, had used EDM never or almost never, a few times (less than 50%), sometimes (approximately 50%), most times (over 50%) and always or almost always. The responses were changed into a numerical scale with the value of 0 given to the had not had sex option, and the value of 5 to the always or almost always option. These items were created specifically for the current study. Erectile dysfunction during first intercourse experience. The participants indicated whether the following items were true concerning their first intercourse experience: passing erection problems, erection problems that precluded penetration, erection problems that precluded ejaculation and fear of losing erection. The response options were true and not true. This measure was created specifically for the current study. Current erectile function. To investigate problems with erectile function, the brief version of the IIEF was used. 13 The IIEF is an originally a 15-item selfreport questionnaire designed to measure five aspects of male sexual behavior and function: erectile function, intercourse satisfaction, orgasmic function, sexual desire and overall satisfaction. Overall, the IIEF has been shown to have excellent reliability (Cronbach s a ¼ 0.91) with the items measuring erectile function having alphas between 0.91 and 0.96. Test retest reliability was also high (r ¼ 0.82). 13 In its abbreviated form, the IIEF-5, five items designed to measure only erectile function have been chosen; erection confidence, erection firmness, erection maintenance, erection maintenance frequency and intercourse satisfaction. The IIEF-5 has been shown to be an equally reliable diagnostic tool. 14 Unrestricted sexual behavior. Three items from the Sociosexual Orientation Inventory (SOI), 17 were used to assess differences in the sexual behavior of the participants. Since its introduction, the SOI has acquired great international acknowledgement and it has been widely used in various studies of basic human mating strategies. 18. The three items were: Number of partners in past year: With how many different partners have you had sexual intercourse within the past year?, Number of partners foreseen: With how many different partners do you realistically foresee having sexual intercourse during the next five years? and Number of one-night stands: With how many different partners have you had sexual intercourse on one and only one occasion?. There were 89 responses exceeding the value of 50 on these open-ended items and these were recoded into the value of 50 to avoid a distributional skew due to extreme scores. In addition, we used an item assessing the age (in years) at which the participants had experienced their first intercourse to explore differences in unrestricted sexual behavior. More than one ejaculation during a single sexual encounter. The participants indicated in what proportion of their sexual interactions they had received more than one ejaculation. The response options were never or almost never, a few times (less than 50%), sometimes (approximately 50%), most times (over 50%) and always or almost always. The responses were changed into a numerical scale with the value of 1 given to the never or almost never 593

594 option, and the value of 5 to the always or almost always option. This item was created specifically for the current study. Confidence in ability to gain and hold erections. The participants indicated the level of their trust in their ability of gaining and holding erections during the past 4 weeks. The response options were very low, low, moderate, high and very high. These responses were changed into a numerical scale with the value of 1 given to the very low and the value of 5 to the very high option. This item was taken from the (IIEF). 13 Statistical analyses Both the group comparisons and association analyses were conducted with the General Linear Model of the SPSS for Windows (version 14) Complex Samples module. This module takes into account the dependence between the members of the same families that was a feature of our sample as it included several siblings from the same families. If such dependence is not taken into account, the variance within a group is underestimated. The R 2 effect size estimates from these analyses were reported to indicate the proportion of variance explained by the independent variables. For association analyses, both Pearson correlations (r p ) as well as regression coefficients (B) with associated standard errors (s.e.) were reported. In all analyses, age was used as a covariate. No other covariates were included. Results Of the participants, 96.5% (n ¼ 4274) had not used EDM, 2.6% (n ¼ 115) had used it for recreational purposes and 0.9% (n ¼ 39) had been prescribed EDM to treat ED. Use of EDM was not related to homosexual experience with 8.5% of non-users, 15.0% of medicinal users and 11.4% of recreational users reporting such experience (Po0.381). Similarly, use of EDM was not related to having a regular sexual partner with 70.5% of non-users, 85.0% of medicinal users and 76.8% of recreational users having a regular sexual partner (Po0.210). The groups differed significantly in terms of age, F(2, 3487) ¼ 12.73, Po0.001, R 2 ¼ 0.005. The participants who had not used erection medication were youngest (M ¼ 29.42, s.e. ¼ 0.12), medicinal users were oldest (M ¼ 33.28, s.e. ¼ 1.06) with recreational users in between the other two groups (M ¼ 31.61, s.e. ¼ 0.59). However, medicinal and recreational users did not differ significantly from each other even though both these groups differed from the non-user group. All following analyses were computed using age as a covariate. Of EDM users, 6.5% had not had sex, 64.1% had used EDM never or almost never, 16.3% a few times (less than 50%), 2.6% sometimes (approximately 50%), 2.6% most times (over 50%) and 7.8% always or almost always during the past 4 weeks. Recreational users (M ¼ 2.33, s.e. ¼ 0.09) had used EDM less often during the past 4 weeks compared to medicinal users (M ¼ 3.18, s.e. ¼ 0.27), F(1, 147) ¼ 8.26, Po0.005, R 2 ¼ 0.143. Medicinal users reported more of all ED indicators during their first intercourse compared to both nonusers and recreational users whereas recreational users reported lower levels than non-users for three of the four indicators (Table 1). The differences between the groups were only significant for passing erectile problems. There were significant differences between the groups in current erectile function, F(1, 3471) ¼ 5.63, Po0.004, R 2 ¼ 0.042. Recreational users had best current erectile function (M ¼ 19.98, s.e. ¼ 0.50), followed by non-users (M ¼ 18.87, s.e. ¼ 0.12) and medicinal users (M ¼ 16.36, s.e. ¼ 1.04). All groups differed significantly from each other. The frequency of use was not associated with current erectile function in either the recreational or the medicinal user groups. Recreational users had significantly more partners in the past year and had more one-night stands than both non-users and medicinal users (Table 2). They also expected to have a significantly higher number of partners during the next 5 years compared to nonusers. They had also experienced their first intercourse at a younger age compared to the other two groups. Non-users and medicinal users did not differ in any of the four variables reflecting an unrestricted sociosexual behavior. Table 1 Occurrence of indicators of erectile dysfunction in association with first intercourse among non-users, medicinal users and recreational users of erection dysfunction medication Overall occurrence Non-users Medicinal users Recreational users w 2 Fear of erectile problems 23.5 23.6 40.0 16.4 4.90** Passing erectile problems 18.4 18.2 42.1 19.4 7.18* Erectile problems that hindered penetration 7.1 7.2 10.0 3.0 1.99 Erectile problems that hindered ejaculation 9.5 9.5 15.0 7.5 1.03 **Po0.10, *Po0.05.

Table 2 Differences in unrestricted sexual behavior between non-users, medicinal users and recreational users of erection medication Non-users Medicinal users Recreational users 595 M s.e. M s.e. M s.e. F R 2 Age at first intercourse 18.09 a 0.05 18.20 a 0.52 16.56 b 0.29 14.97*** 0.043 Number of partners in past year 1.70 a 0.05 3.04 a,b 1.24 4.84 b 0.87 7.08*** 0.023 Number of partners foreseen 2.98 a 0.09 4.77 a 1.50 8.77 b 1.25 8.42** 0.025 Number of one-night stands 5.10 a 0.16 7.75 a,b 2.32 13.01 b 1.51 14.05*** 0.037 **Po0.01, ***Po0.001. a,b Means with different superscript letters differ from each other significantly (Po0.05) according to simple contrasts. Use of EDM was also related to having more than one ejaculation during a single sexual interaction, F(1, 3148) ¼ 3.84, Po0.022, R 2 ¼ 0.003. Recreational users also more often experienced more than one ejaculation during one sexual interaction (M ¼ 1.94, s.e. ¼ 0.07) compared to non-users (M ¼ 1.71, s.e. ¼ 0.01) but not compared to medicinal users (M ¼ 1.80, s.e. ¼ 0.19). Medicinal users and nonusers did not differ from each other. Medicinal users had the lowest confidence in their ability to gain and hold erections, followed by recreational users and non-users, F(1, 3455) ¼ 23.59, Po0.001, R 2 ¼ 0.022 (Figure 1). Planned simple contrasts showed that all three groups differed significantly from each other. The frequency of using EDM was related to the level of confidence in ability to gain and hold erections both among medicinal users r p ¼ 0.52, B ¼ 0.38, s.e. ¼ 0.10, t ¼ 3.63, Po0.001, R 2 ¼ 0.266 and among recreational users r p ¼ 0.24, B ¼ 0.20, s.e. ¼ 0.10, t ¼ 2.01, Po0.045, R 2 ¼ 0.059. In both groups, more frequent use of EM was associated with less confidence in ability to gain and hold erections. Age as such was not related to the confidence variable, r p ¼ 0.03, B ¼ 0.00, s.e. ¼ 0.00, t ¼ 1.67, Po0.095, R 2 ¼ 0.001, suggesting that there was no overall trend toward lowered confidence. Those having a regular sexual partner were more confident with their erection (M ¼ 3.53, s.e. ¼ 0.02) than those without such a partner (M ¼ 3.01, s.e. ¼ 0.03), F(1, 2390) ¼ 186.63, Po0.001, R 2 ¼ 0.079. Discussion Recreational use of EDM was more common than medicinal use in this population-based sample of 18 to 44-year-old men. This is in line with previous research showing that a majority of respondents had obtained their EDM from sources other than healthcare providers. 9,10 However, Musacchio, Hatrich and Garofalo still reported that a majority of their respondents had used EDM to treat problems with erectile function. 9 In the current study, the proportion of participants reporting recreational use was Mean Confidence 5.00 4.00 3.00 2.00 1.00 0.00 Non-Users Medicinal Users Use Of Erection Medication Error bars: +/- 1 SD Recreational Users Figure 1 Confidence in ability to gain and hold erections among non-users, medicinal users and recreational users of erection medication. relatively high 2.6%, suggesting that any adverse psychological effects of recreational use would affect a significant numbers of men. In addition, since the participants were asked to report whether they had used EDM during the previous 4 weeks, the number of users would probably have been even higher with a longer time range. As ED is strongly age-related, 19 these results should be interpreted considering that the mean age of the sample were below 30 years. In an older sample, medicinal use would probably be higher. One of the issues we wanted to investigate was whether the men who reported using EDM for recreational purposes actually differed from medicinal users. The findings seemed to support the veracity of the participants self-reports. Recreational users reported less problems with erectile function during their first intercourse compared to both medicinal and non-users. Of course, we cannot be totally certain that the participants had not used EDM already during their first intercourse experience, but we hold this to be unlikely. Especially interesting is the finding that only 16% of recreational users reported fear of erectile problems compared to 40% of medicinal users and 24% of non-users at the time of their first intercourse. This

596 suggests that to begin with, before using EDM, the recreational users were quite confident in their ability to gain and hold their erections. Also, recreational users had best current erectile function whereas medicinal users had the worst functioning. Further, recreational users were sexually more unrestricted compared to non-users and, in terms of the expected number of future partners, also compared to medicinal users. They had also experienced their first intercourse at a younger age. In addition, recreational users reported experiencing more than one ejaculation more often than nonusers. This finding probably reflects the fact that prolonging sexual encounters is one of the reasons for recreational use of EDM. Overall, the findings indicate that recreational users differ from both nonusers and medicinal users in a way that supports the veracity of their self-report regarding the motivation for their use of EDM. We did not find an overrepresentation of men with homosexual experience among the users probably reflecting the fact that our study was based on a population sample. The main aim of the present study was to see if recreational use of EDM would adversely affect the confidence the users had in their ability to gain and hold erections. The findings seemed to support this hypothesis although causality cannot be proven in a correlational study. Recreational users had lower levels of confidence compared to non-users. A change seems to have taken place compared to when the participants started their sexual activity as recreational users at that time were the most confident group in terms of their erectile function as pointed out above. Of course, in the present research design, it is not possible to exclude other intervening factors besides recreational use of EDM that might have adversely affected the confidence of this group. However, as all other indicators suggest that this group is enjoying good erectile function and being sexually more active than the other groups, a causal effect created by EDM remains the most logical explanation. The result is also not explained by a general age-related decrease in confidence in maintaining erections as age was not related to the confidence variable. Further, even though having a regular sexual partner was associated with higher confidence, using EDM was not related to this partnership status. In addition, the more frequent the recreational use of EDM was, the less confident the participants were in their erectile ability. This further supports the possibility that the use of EDM has affected the confidence level of the participants. As lack of confidence in one s ability to gain and hold erections has been identified as an important psychogenic risk factor for ED, 14 the findings have important implications. Recreational users of EDM may be vulnerable for becoming psychologically dependent on pharmacologically induced erection. However, it should be noticed that the associations detected are small in absolute terms. Certainly, the results suggest that there is a need for longitudinal follow-up studies of young men who start using EDM for recreational purposes. References 1 Rosen RC. Prevalence and risk factors of sexual dysfunction in men and women. Curr Psychiatry Rep 2000; 2: 189 195. 2 Kubin M, Wagner G, Fugl-Meyer AR. Epidemiology of erectile dysfunction. Int J Impot Res 2003; 15: 63 71. 3 Hanash K. Comparative results of goal oriented therapy for erectile dysfunction. J Urol 1997; 157: 2135 2138. 4 Mulhall JP, McLaughlin TP, Harnett JP, Scott B, Burhani S, Russell D. Medication utilization behavior in patients receiving phosphodiesterase type 5 inhibitors for erectile dysfunction. J Sex Med 2005; 2: 848 855. 5 Kleinplatz PJ. Sex therapy: how do sex therapists think about and deal with sexual problems? In: McAnulty RD, Burnette MM (eds). Sex and Sexuality. Volume 2: Sexual Function and Dysfunction. Praeger: London, 2006, pp 176 211. 6 Fink H, MacDonald R, Rutks I, Wilt TJ. Sildenafil for the treatment of erectile dysfunction: a systematic review. Arch Intern Med 2002; 95: 1349 1360. 7 Goldstein I, Lue TF, Padma-Nathan H et al. Oral sildenafil in the treatment of erectile dysfunction. Sildenafil study group. New Engl J Med 1998; 338: 1397 1404. 8 Aldridge J, Measham F. Sildenafil (Viagra) is used as a recreational drug in England. BMJ 1999; 318: 669. 9 Mussachio NH, Hatrich MH, Garofalo R. Erectile dysfunction and Viagra use: what s up with college-age males. J Adolesc Health 2006; 39: 452 454. 10 Kim A, Kent CK, Klausner JD. Increased risk of HIV and sexually transmitted disease transmission among gay or bisexual men who use Viagra, San Francisco 2000 2001. AIDS 2002; 16: 1425 1428. 11 Sherr L, Bolding G, Maguire M, Elford J. Viagra use and sexual risk behaviour among gay men in London. AIDS 2000; 14: 2051 2053. 12 Brewer Auld R, Brock G. Sexual and erectile dysfunction: results of a national survey. J Sex Reprod Med 2002; 2: 50 54. 13 Rosen R, Riley A, Wagner G, Osterloh I, Kirkpatrick J, Mishra A. The Int index of erectile function (IIEF): a multidimensional scale for assessment of erectile function. Urology 1997; 49: 822 830. 14 Rosen RC, Cappelleri JC, Smith MD, Lipsky J, Peña BM. Development and evaluation of an abridged, 5-item version of the Int Index of Erectile Function (IIEF-5) as a diagnostic tool for erectile dysfunction. Int Impot Res 1999; 11: 319 326. 15 Zilbergeld B. The New Male Sexuality. Bantam Books: New York, 1999. 16 Klotz T, Sachse R, Heidrich A, Jockenhövel F, Rohde G, Wensing G et al. Vardenafil increases penile rigidity and tumescence in erectile dysfunction patients: a RigiScan and pharmacokinetic study. World J Urol 2001; 19: 32 39. 17 Simpson JA, Gangestad SW. Individual differences in sociosexuality: evidence for convergent and discriminant validity. J Pers Soc Psychol 1991; 60: 870 883. 18 Schmitt DP. Sociosexuality from Argentina to Zimbabwe: a 48- nation study of sex, culture, and strategies of human mating. Behav Brain Sci 2005; 28: 247 311. 19 Feldman HA, Goldstein L, Hatzichrisou DG, Krane RJ, McKinlay JP. Impotence and its medical and psychosocial correlates: results of the Massachusetts male aging study. J Urol 1994; 151: 54 61.