Should you prioritise mental health?
Ultimately, you should prioritise the problem that you think will allow you to do the most good with your spare resources (your time and money). There are a large number of open-ended questions which need to be resolved before we can determine how we do the most good. This section sets out some of the crucial considerations but does not attempt to answer them.
What is of intrinsic value?
We have suggested that a particular mental health charity might be more cost-effective at increasing happiness than at least one of the global development charities GiveWell recommend. Presumably, happiness, a positive balance of enjoyment over suffering, is one of the things that is intrinsically good, that is, good in itself. Some (including the Happier Lives Institute), believe it is the only intrinsic good.
If you believed there were other intrinsic goods, that would potentially change the priorities. Suppose you thought autonomy, equality and happiness were all valuable in themselves. As a result, you might, perhaps, think poverty is more important than mental health on the grounds poverty alleviation increases autonomy and equality whereas improving mental health does not.
However, such a conclusion might be a bit too quick. Even if you value things other than happiness, a mental health intervention might, from the point of view of your moral theory, still do the most good. You could believe targeting mental illness is just as autonomy-enhancing or equality-increasing as alleviating poverty, given how disabling it can be to be depressed, anxious, etc. Or, even if treating mental health does a poor job at promoting autonomy and equality, you might think that it does a good enough job of increasing happiness, something that you, presumably, value anyway, so as to compensate for its apparent lack of effect on other values. Hence, it’s important to consider what the goods are and, if there is more than one, how they are weighed.
Do only some people matter morally, such as those currently alive, or does everyone who could ever live matter?
The (mathematically) simplest view in population ethics is totalism, which holds the best outcome is the one with the greatest sum total of well-being of everyone - past, present, and future. On totalism, all possible people matter and it’s good to create happy lives.
In contrast, many people intuitively hold a ‘person-affecting’ view of population ethics: while the well-being of those who do (or will) exist matters, there is no value in creating new lives. This is typically justified on the grounds that an outcome can be better or worse because and to the extent that it’s better or worse for persons, and existence can never be better or worse for a person than non-existence. Hence there’s no value in creating new lives, as being created is not good for anyone. We might say, of a particular person who could exist in (say) 10,000 years, that they don’t miss out on never having existed. Much of this is captured by Jan Narveson’s famous slogan “We are in favor of making people happy, but neutral about making happy people.” 
One particular person-affecting view is necessitarianism, which holds the only people who matter, when choosing between two outcomes, are those that are going to exist whatever we choose to do (i.e. exist necessarily). On this view, we still count the future people who will exist anyway. However, in practice, it’s unlikely there are many necessary, future people. The identities of who comes into existence depends, among other things, on whom the genetic parents of someone happen to be. Given the nature of human reproduction, if your parents had had sex a moment earlier, or later, then someone else would almost certainly have been born instead. Plausibly, even small changes in the world are likely to change who gets conceived and thus alter the identities of future people. As a result, necessitarians will think our moral concerns are, in effect, restricted to those who presently exist.
Whether you take a ‘person-affecting’ view (e.g. necessitarianism) or an ‘impersonal’ view (e.g. totalism) will be a very important consideration in prioritising what to do. There are other views in population ethics, but it would be an unnecessary diversion to discuss those here. Some causes, such as reducing existential threats to humanity (e.g. from AI) or improving animal welfare (e.g. by reducing factory farming) primarily affect future sentient beings rather than those alive today. By contrast, while alleviating the mental illness or reducing the poverty of those alive today will have some effect on future people, presumably their main impact is that they benefit the present generation.
Which is the most plausible view? Population ethics is a notoriously problematic area, where all of the views can be shown to have apparently implausible implications. This is not a topic we can deal with here.
Empirical and personal complications
Simply settling your moral views is not sufficient to tell you what to prioritise; there are many empirical considerations too. For example, you could hold a person-affecting view but still conclude that reducing existential risks is the top priority simply based on the risk they pose to the present generation.
Or, you could hold totalism - and therefore accept that it would be good, in theory, to make progress on animal welfare and shaping the far future - but nevertheless think, in practice, you can do more good by focusing on something in the near-term, such as mental health or global development instead. You might reach this conclusion if you held some of the following beliefs:
Finally, you could decide that making currently existing humans lives happier is how you can do the most good, but disagree that mental health is the top priority. Mental illness is not the only source of unhappiness. If we could wave a magic wand and fully treat all mental health conditions, the world would not be at maximum happiness. Other stand-out areas of focus for increasing life satisfaction are:
If this cause profile has motivated you to use some of your resources towards addressing the large and neglected problem of mental health then there are a number of ways you can contribute. Go to our Take Action section to learn more about your options for donating to effective organisations, pursuing a career in mental health or assisting with further research.
 For a summary of the problems of population ethics, see Greaves, H. (2017) “Population Axiology.” Philosophy Compass, 12(11), e12442. Note Greaves is unsympathetic to person-affecting views.
 Narveson, J. (1973). “Moral Problems of Population,” The Monist, 57(1), 62–86.
 See Part 4 in Parfit, D. (1987). Reasons and persons. Oxford: Clarendon Press
 Arrhenius, G. (2000). “An Impossibility Theorem for Welfarist Axiologies,” Economics & Philosophy, 16(2), 247–66.
 Lewis, G. (2018). “The Person-Affecting Value of Existential Risk Reduction,” Effective Altruism Forum.
 Felicia Marie Knaul et al. (2017). “Alleviating the Access Abyss in Palliative Care and Pain Relief-an Imperative of Universal Health Coverage: The Lancet Commission Report.” The Lancet, 391(10128), 1391-1454.