The goal of this study was to compare the prevalence rates of loneliness between individuals who are dependent on methamphetamine and those who are not dependent on methamphetamine, and evaluate the impact of loneliness on risky sexual beliefs and poor intentions to practice safer sex. We hypothesized that individuals who are dependent on methamphetamine would have higher rates of loneliness than those not dependent on methamphetamine. Furthermore, we hypothesized that loneliness would be associated with riskier beliefs and riskier intentions about sex, such that individuals with high rates of problematic loneliness would endorse poorer personal norms about practicing safer sex and poorer intentions to practice safer sex, particularly among methamphetamine dependent individuals. The study was conducted at the University of California San Diego Translational Methamphetamine AIDS Research Center from June 2014 to June 2017 after receiving approval from its Institutional Review Board. The current study was conducted as a sub-study of a large, center-wide project examining the intersection of methamphetamine and HIV on the central nervous system and behavior, particularly given the established independent effects of methamphetamine and HIV on the CNS , as well as the link between methamphetamine use and HIV risk . This larger project sought to study individuals whose methamphetamine use exceeded a particular exposure-threshold to methamphetamine ; however, recruitment was kept broad to best generalize findings. Therefore, participants were not required to be in a particular stage of their addiction to participate . Rather, participants were recruited from the greater San Diego community, a primarily an urban city located near the southwest U.S. border. Specific recruitment locations included substance abuse treatment programs, HIV clinics, and the broader community. Recruitment methods included hosting community education events, using social marketing to promote the research study, and engaging in a wide range of community outreach venues . After providing written, informed consent,greenhoues growing racks participants underwent a comprehensive, standardized neurobehavioral and neuromedical assessment. Inclusion criteria were broad and encompassed any individuals aged 18 or older from the local community who were able to complete in-person study assessments. Exclusion criteria included prior histories of neurological or severe psychiatric conditions that are independent of methamphetamine and/or HIV infection.

Participants included 115 English-speaking adults stratified by whether or not they met the Diagnostic and Statistical Manual of Mental Disorders 4th edition criteria for lifetime methamphetamine dependence and methamphetamine abuse or dependence ≤ 18-months prior to study enrollment . If individuals did not meet both these criteria, then they were placed in the control group: . The DSM-IV was used to assess participants instead of the DSM-5 in order to maintain protocol consistency with other ongoing research projects that were being conducted at our center and had already been developed and executed prior to DSM-5 publication. Thus, the use of DSM-IV allowed for comparisons between other center-wide studies and their cohorts. Criteria for the METH+ group were chosen in order to capture individuals who experienced both severity and recency of methamphetamine use-related problems. An 18-month time frame for classifying recent/current methamphetamine abuse or dependence was selected to match DSM-IV’s clinical diagnostic time frame as closely as possible, while also balancing the feasibility of participant recruitment. Three individuals in the METH− group reported limited and/or remote methamphetamine use, which did not meet DSM-IV criteria for abuse or dependence. All three individuals were older adults with at least a high school education. Two of the three individuals were Black , two were HIV−, and two were male. The age of first methamphetamine use among these three individuals ranged from 30–41 years , their time since last methamphetamine use ranged from about 1-month to > 25 years , their total lifetime methamphetamine use ranged from about 3- to 9-months , and their total lifetime quantity of methamphetamine use ranged from about 6 g to 1.8 kg . Individuals meeting criteria for non-methamphetamine substance dependence could have been enrolled in the study if they last met criteria > 5 years prior to study enrollment. Similarly, individuals meeting non-methamphetamine substance abuse criteria could have been enrolled in the study if they last met criteria > 12-months prior to study enrollment. Due to high prevalence of alcohol and cannabis use histories in our overall sample , individuals meeting criteria for alcohol or cannabis abuse or dependence were enrolled, provided that criteria for dependence had last been met > 12-months prior to study enrollment. Per these criteria, only one person in each METH− and METH+ group met criteria for current, non-methamphetamine substance use disorder . In the overall sample, 58% were people with HIV, which was established by self-report and confirmed by the Miriad HBc/HIV/HCV finger stick point-of-care test . Table 1 summarizes other relevant participant characteristics in each METH group, and Table 2 summarizes the DSM-IV-TR diagnostic criteria for methamphetamine abuse and dependence. Demographic characteristics and scores on the aforementioned behavior scales were compared between the METH−/+ groups using t-tests for continuous variables and Pearson Chi 2 tests, or Fisher’s Exact Test for dichotomous or nominal variables. Non-parametric Spearman’s ρ was used to examine univariable associations with loneliness given the non-normal distribution of scores.

Multi-variable linear regression was used to investigate the association between loneliness and METH−/+ groups, as well as the association between loneliness and sexual risk norms and intentions. Participant characteristics from Table 1 were selected as covariates in the multi-variable regression if they significantly differed between METH−/+ groups using a critical α-level of .05 . Lifetime history of mood disorder and social support network were also considered as covariates given their significant associations with the primary outcome variables . Due to high collinearity between premorbid verbal IQ and years of education, the former was selected as the model covariate given its robustness to other potential confounds . Though HIV serostatus and neurocognitive impairment were unrelated to loneliness in our overall sample, they were selected as covariates because of prior literature supporting their associations with loneliness . In our overall sample, people with HIV also were more likely to have engaged in riskier sexual behaviors over the past 6-months and prior to the past 6-months compared to HIV− individuals. Additionally, although 98.5% of people with HIV were on antiretroviral therapies and 82.3% had undetectable viral loads that were unassociated with poorer norms or poorer intentions to practice safer sex, HIV+ serostatus was associated with poorer intentions to practice safer sex in the whole sample, thereby providing support to include HIV serostatus as a covariate during analyses. Statistical significance was determined using a critical α-level of .05 for all analyses. The Spearman ρ correlations between loneliness and continuous variables in METH− and METH+ groups are listed in Table 3, as well as results of one-way ANOVAs comparing loneliness across categorical variables. There was a significant, omnibus difference in loneliness across people of different ethnicities in the METH−, but not in the METH+ group. Among METH− individuals, Black participants reported the highest loneliness , while other/Hispanic participants were the least lonely . Those with a lifetime history of mood disorder reported significantly higher loneliness compared to those without , but only within the METH− group. In the METH+ group, people with HIV were significantly lonelier than HIV− individuals ; there was no HIV effect on loneliness in the METH− group. The only non-methamphetamine use disorder that was associated with loneliness was lifetime history of opioid use disorder; however, this association was only noted in the METH+ group. Specifically, those in the METH+ group with a lifetime history of opioid use disorder reported lower loneliness relative to METH+ individuals without lifetime history of opioid use disorder. Greater norms about practicing safer sex and greater intentions to practice safer sex were each significantly associated with lower current sexual risk in both groups . In a multi-variable regression with only METH+ individuals, potentially problematic levels of loneliness and neurocognitive impairment remained significantly associated with poorer beliefs about practicing safer sex after controlling for age, HIV serostatus, lifetime history of mood disorder, lifetime history of other substance use disorder, age of first methamphetamine use, and total number of people in social support network . In METH− individuals, this model was not significant. Findings remained unchanged when lifetime history of other substance use disorders was replaced with the more specific lifetime history of opioid use disorder variable. In addition,grow drying rack our results held regardless of the recency of participants’ methamphetamine use, which could also serve as a proxy for recruitment source . In METH+ individuals, potentially problematic levels of loneliness and HIV+ serostatus remained significantly associated with poorer intentions to practice safer sex after controlling for age, neurocognitive impairment, premorbid verbal IQ, lifetime history of mood disorder, lifetime history of other substance use disorders, age of first methamphetamine use, and total number of people in social support network . In METH− individuals, this model was not significant. Again, findings remained unchanged when lifetime history of other substance use disorders was replaced with lifetime history of opioid use disorder, and when recency of methamphetamine use was considered.

Given prior literature suggesting the role of impulsivity/disinhibition in the relationship between loneliness and sexual risk behavior , the effect of impulsivity/disinhibition on poorer beliefs about and intentions to practicing safer sex was also considered. In the overall sample, higher impulsivity/disinhibition was associated with having potentially problematic levels of loneliness , regardless of methamphetamine status. However, impulsivity/disinhibition did not reach statistical significance when predicting beliefs about practicing safer sex or intentions to practice safer sex after controlling for HIV serostatus, methamphetamine status, potentially problematic loneliness, and the interaction between methamphetamine status and potentially problematic loneliness. The interaction between methamphetamine status and potentially problematic loneliness was a significant contributor of both beliefs about practicing safer sex and intentions to practice safer sex . HIV-positive serostatus was also a significant contributor of poorer intentions to practice safer sex , but not beliefs about practicing safer sex. There was no significant interaction between HIV and methamphetamine status on intentions to practice safer sex. Figures 2 and 3 illustrate the interactive effect between potentially problematic loneliness and methamphetamine on norms and intentions to practice safer sex. Our findings indicate that individuals with methamphetamine use disorders reported higher levels of loneliness than those in a METH− comparison group, consistent with prior reports , although previous work is limited. Our cross-sectional results cannot disentangle directionality of this relationship, but it is presumed to be bidirectional: loneliness may predispose people to methamphetamine use, and methamphetamine use may have severe social consequences that contribute to loneliness. Increased loneliness in METH+ compared to METH− individuals held despite comparable levels of exposure to factors associated with loneliness . In fact, 50% of the METH+ group met criteria for problematic levels of loneliness, highlighting a potential need for psychological intervention, compared to about 30% in the METH− group. The presence of loneliness also may result in poorer personal norms and intentions about practicing safer sex, possibly as a means of emotional pain and distress avoidance through pleasure-seeking behaviors, resulting in the potential to engage in unsafe sexual behaviors. As such, loneliness can have indirect, downstream public health implications in a population already at high risk for engaging in riskier behaviors . In the general population, loneliness is a significant risk factor for many negative health consequences such as cognitive decline and cardiovascular risk . In people with HIV, loneliness has been associated with poorer immune function , more depressive symptoms , and lower CD4+ count . Recent work has highlighted the association between loneliness and substance use and dependence such as opioid use disorder , alcohol use disorder , and co-occurring addictive disorders such as gambling and internet addiction . Our study extends this research to illustrate that among individuals who are dependent on methamphetamine, loneliness is also associated with riskier beliefs and intentions about practicing safer sex, above and beyond the impact of other pertinent factors. The higher prevalence of loneliness in methamphetamine users, and its association with riskier beliefs and intentions about practicing safer sex, may be explained by some of the following aspects specific to methamphetamine addiction : positive reinforcement , negative reinforcement , inhibitory control dysfunction , incentive salience , and stimulus response learning .