Prosocial behavior can increase happiness in the short term but decrease it in the long term.

From Falk and Graeber:  

Significance

Governments around the world increasingly acknowledge the role of happiness as a societal objective and implement policies that target national wellbeing levels. Knowledge about the determinants of happiness, however, is still limited. A longstanding candidate is prosocial behavior. Our study empirically investigates the causal effect of prosocial behavior on happiness in a high-stakes decision experiment. While we confirm previous findings of a positive effect in the short term, our findings distinctly show that this effect is short lived and even reverses after some time. This study documents that prosocial behavior does not unequivocally increase happiness because prosocial spending naturally requires giving up something else, which may decrease happiness in its own right.

Abstract

Does prosocial behavior promote happiness? We test this longstanding hypothesis in a behavioral experiment that extends the scope of previous research. In our Saving a Life paradigm, every participant either saved one human life in expectation by triggering a targeted donation of 350 euros or received an amount of 100 euros. Using a choice paradigm between two binary lotteries with different chances of saving a life, we observed subjects’ intentions at the same time as creating random variation in prosocial outcomes. We repeatedly measured happiness at various delays. Our data weakly replicate the positive effect identified in previous research but only for the very short run. One month later, the sign of the effect reversed, and prosocial behavior led to significantly lower happiness than obtaining the money. Notably, even those subjects who chose prosocially were ultimately happier if they ended up getting the money for themselves. Our findings revealed a more nuanced causal relationship than previously suggested, providing an explanation for the apparent absence of universal prosocial behavior.