Prosocial effects of MDMA: A measure of generosity

This placebo-controlled within-subjects study (n=32) investigated the dose-dependent effects of MDMA (35-70mg/70kg) on generosity, as measured by their willingness to trade-off personal welfare in favor of the welfare of someone else. The higher dose of MDMA increased generosity in relation to a close friend but not a stranger, whereas the lower dose did not affect generosity toward the friend but slightly increased generosity toward a stranger. These results are in line with the prosocial effects of oxytocin, which promotes trust amongst members of a social ingroup but not the out-group.

Abstract

“Background: 3,4-methylenedioxymethamphetamine (MDMA) produces “prosocial” effects that contribute to its recreational use. Few studies have examined the cognitive and behavioral mechanisms by which MDMA produces these effects. Here we examined the effect of MDMA on a specific prosocial effect, i.e. generosity, using a task in which participants make decisions about whether they or another person will receive money (Welfare Trade-Off Task; WTT).

Methods: The project included one study without drug administration and one with MDMA. In Study 1, we administered the WTT to healthy adults (N = 361) and examined their performance in relation to measures of personality and socioeconomic status. In Study 2, healthy volunteers with MDMA experience (N = 32) completed the WTT after MDMA administration (0, 0.5, or 1.0 mg/kg).

Results: As expected, in both studies participants were more generous with a close friend than an acquaintance or stranger. In Study 1, WTT generosity was related to household income and trait Agreeableness. In Study 2, MDMA (1.0 mg/kg) increased generosity toward a friend but not a stranger, whereas MDMA (0.5 mg/kg) slightly increased generosity toward a stranger, especially among female participants.

Conclusions: These data indicate that the WTT is a valuable, novel tool to assess a component of prosocial behavior, i.e. generosity to others. The findings support growing evidence that MDMA produces prosocial effects, but, as with oxytocin, these appear to depend on the social proximity of the relationships. The brain mechanisms underlying the construct of generosity, or the effects of MDMA on this measure, remain to be determined.”

Authors: Matthew Kirkpatrick, Andrew W. Delton, Theresa E. Robertson & Harriet de Wit

Summary

Introduction

3,4-methylenedioxymethamphetamine (MDMA) or “ecstasy” reportedly produces prosocial effects, including feelings of empathy for others. A novel task based on evolutionary theories of valuation and welfare trade-offs was used to assess the tendency to make decisions that increase the welfare of one organism at the expense of another.

Few studies have examined effects of drugs on generosity. However, oxytocin, a neuropeptide, has been shown to increase generosity in several studies, and MDMA has also been shown to increase generosity in the Welfare Trade-Off Task.

In order to estimate the Welfare Trade-Off Ratio, subjects must decide whether they or another person will receive money. The ratio of the values is manipulated across decisions, so that subjects must decide whether they or another person will receive $5, $10, or $15.

MDMA produces prosocial effects, including generosity, in participants. Few studies have examined the cognitive and behavioral mechanisms by which MDMA produces these effects.

The WTT is based on earlier research that extended temporal discounting procedures to social discounting. It found that subjects made interpersonal trade-offs according to the same equation that describes inter-temporal trade-offs.

The WTT is a well-suited measure of generosity in a laboratory-based study of drug effects. It correlates with several well-understood rating scale measures of similar prosocial constructs, including valuing the welfare of close others and psychological closeness and overlap.

We administered the WTT to 361 healthy young adults and examined their WTT performance in relation to age, gender, socioeconomic status, and personality. We also assessed the effects of MDMA (0.5 and 1.0 mg/kg) and placebo on the WTT.

Trade-Off Task

Participants were recruited through online advertisements, flyers on community bulletin boards, and word-of-mouth referrals. They underwent a brief psychiatric screening interview and were age 18-35 and Caucasian.

361 volunteers completed Study 1, 57% of whom were female. They were mean SD 23.2 3.3 years old, had completed 15.4 1.7 years of formal education, and were regularly drinking alcohol, smoking marijuana, and smoking tobacco.

Design and procedure

Participants completed questionnaires and tasks during a single visit to the laboratory, and were instructed to abstain from alcohol, marijuana, and other recreational drugs for 24 hours before the session.

Measures

The Neuroticism Extraversion Openness Five Factor Inventory was used to assess personality traits. Agreeableness was positively correlated with WTT generosity, while Neuroticism, Extraversion, Openness, and Conscientiousness were unrelated.

Participants were split into four income groups based on relatively equal group sizes: less than $20,000, $20,000 – $40,000, $40,000 – $80,000, and > $80,000.

Participants answered six series of questions about two individuals and were asked to decide whether to give or receive money. The amount to be given to the other person was anchored at a single value and was systematically varied to create 10 WTRs. Table 1 shows one set of WTT decisions used to create a WTR. The midpoint between the two question ratios is used to calculate the WTR.

A person’s willingness to trade off money is influenced by their WTR toward another person. A higher WTR implies greater levels of generosity.

Data analysis

We conducted a paired t-test and two multiple regressions to investigate whether individuals were more generous to the Friend than to the Acquaintance. The predictors were the three demographic variables, five trait personality variables, and the welfare trade-off switch points.

Study 2: Effects of MDMA on Welfare Trade-Off Task

Participants were healthy men and women aged 18 – 30 who had used MDMA 4 – 80 times in their lifetime. They underwent an in-person psychiatric evaluation and medical examination, including an electrocardiogram and physical examination.

Participants were told they could receive a stimulant, sedative, cannabinoid, or placebo. They were instructed to consume their normal amount of caffeine, but were asked to refrain from tobacco use for 9 hours, and other drug use for 48 hours, prior to each session.

32 volunteers completed the study; nine female, 23 male, one Asian, five Black, five Hispanic, one Mixed, 20 White, and one daily tobacco smoker. They had used MDMA a mean of 17.0 times.

Design

The study used a within-subjects design with two doses of MDMA and placebo. Participants completed three outpatient sessions separated by at least 5 days as a washout period.

Procedure

Participants provided urine and breath samples to confirm abstinence from alcohol, amphetamine, cocaine, and opiates, and women were tested for pregnancy. At 09:30, participants ingested capsules containing either MDMA or placebo, and physiological and subjective measures were obtained at 10:30, 11:00, 11:30, 13:00, and 13:30.

Measure

We used a similar version of the Welfare Trade-Off Task in Study 1 to examine the effects of MDMA on generosity toward a stranger.

Drug

MDMA powder was administered in randomized order, under double-blind conditions, in size 00 opaque capsules with lactose filler. Placebo capsules contained only lactose.

Data analysis

MDMA had acute effects on generosity in WTT switch point data. There were sex differences in MDMA responses, which were assessed with post hoc comparisons.

Results

Study 1

The Welfare Trade-Off Task revealed that participants were more generous toward the Friend compared to the Acquaintance. The most parsimonious significant model included Agreeableness and Income group only.

Figure 1 shows that higher Agreeableness scores were associated with greater generosity, and that this effect was evident whether the other person was a close friend or an acquaintance.

Figure 2 shows that welfare trade-off switch points were related to income. Participants with a lower household income were more generous to an Acquaintance, but this relationship did not hold true for Friends.

Study 2

Participants were significantly more generous toward the Friend compared to the Stranger, regardless of MDMA dose, and MDMA significantly increased generosity when the other person was the Friend. There were no other significant effects of sex on drug response.

Discussion

These analyses of the WTT showed that participants were more generous with a close friend than an acquaintance or stranger, and that generosity was negatively correlated with household income. Participants high on the personality trait of Agreeableness were more generous toward both close friends and acquaintances.

In Study 1, generosity was negatively related to household income and positively related to the personality measure of trait Agreeableness. The relationship between generosity and agreeableness was intuitively more direct and suggested that a positive disposition also has behavioral consequences on willingness to share financial resources.

We found that MDMA increased generosity, and that this effect depended on the dose and the relational closeness of the other recipient. The most pronounced increase in generosity was observed after the higher dose of MDMA.

MDMA increases levels of oxytocin, a neuropeptide involved in social bonding, and this effect is thought to contribute to its empathogenic effects. Oxytocin can increase generosity toward a close friend but not toward a stranger. MDMA slightly increased generosity to a stranger at a low dose, but it is not clear why. The effects may be due to oxytocin levels or a non-specific drug effect.

Recent clinical studies indicate that MDMA plus psychotherapy produces long-lasting improvements in PTSD symptoms and social relationships.

MDMA increased generosity toward the stranger primarily in women, which is consistent with at least one previous report indicating that MDMA may produce more intense psychoactive effects in women compared to men. However, differences in dose or task design and our relatively small sample size could explain this difference.

The WTT was used to assess a novel behavioral construct, that of generosity to others. Generosity was related to both socioeconomic status and the personality trait of Agreeableness, and MDMA increased generosity.