Even if mental health is a large and neglected problem, it cannot be a priority if there are no effective treatments. The Happier Lives Institute has identified three broad types of treatments for mental health although further research is required to determine which one is the most cost-effective.
While many people’s mental image of this is still Freudian psychoanalysis (“lie down on the couch; tell me about your childhood”), such therapy has been shown to be ineffective and modern medicine has moved on. In fact, there are no randomised trials which have demonstrated psychoanalysis performs better than the natural rate of recovery.
The UK’s National Institute for Health and Care Excellence (NICE) recommends Cognitive Behavioural Therapy (CBT), as the first line treatment for all mental health disorders. CBT involves teaching people how to understand their thoughts and emotions and process them differently. The UK’s Improving Access to Psychological Therapies (IAPT) programme treats 560,000 patients a year, of whom 50% recover and two-thirds show worthwhile benefits.
CBT is best understood as a family of therapies, rather than a single treatment: the CBT procedures for depression and, say, social phobia, share almost no overlap. The latest forms of CBT are a substantial improvement on earlier effective methods. For example, 78% of patients with social anxiety recovered from cognitive treatments, compared with 38% from exposure therapy, which was the original (non-psychoanalytic) procedure used to treat it.  The effects of CBT can be long-lasting, too. A study on CBT recipients found the effects of treatment (compared to usual care with antidepressants), measured in standard mental health scores, were present 4 years later without obviously appearing to reduce over time, as shown in figure 2.  This can be explained by the fact that CBT teaches the patient a skill - how to control and adjust their thought - much like learning to read and write involves learning a skill. So as long as people remember what they’ve learnt, the effect should continue.
CBT is not the only effective psychological therapy: others include mindfulness-based cognitive therapy, interpersonal therapy, and counselling.
Psychological treatments are conventionally delivered face-to-face, either one-on-one or in a group setting. A leading example of a charity in the developing world providing these types of intervention is StrongMinds, which offers interpersonal group therapy to women in Uganda. Such treatments can also be effectively delivered electronically, either via computers or smartphones. As this doesn’t require human interaction, it could potentially be very cheap and scalable.
The best known chemical treatments are antidepressants. Despite controversy, evidence shows they are effective (more so for severe than mild or moderate depression), although they seem to function like painkillers, treating the symptoms without removing the underlying cause(s). This explains why cognitive treatments, unlike antidepressants, reduce the rates of relapse.
There are also some highly promising treatments for mental illnesses that rely on currently illegal recreational drugs. Ketamine may provide substantial short-term relief from depression. MDMA (‘ecstasy’) has recently been labelled a ‘breakthrough drug’ by the FDA in the USA because of its remarkable effectiveness in treating post-traumatic stress disorder. Perhaps most promising of all is the potential of psychedelics, such as LSD and psilocybin (the active ingredient in ‘magic mushrooms’) for treating mental illness. Carhart-Harris et al. (2016) gave a single dose of psilocybin to 12 people with moderate to severe treatment-resistant depression. The subjects had been depressed for a mean average of 17.8 years. After psychedelic-assisted therapy, 67% were classed as non-depressed after 1 week and 42% as non-depressed after 3 months without any further treatment. This is displayed in figure 3.
Stage-2 trials started in September 2018 to test the effectiveness of psilocybin on a larger scale. In October 2018 the FDA granted the 'breakthrough therapy' designation for psilocybin therapy for Treatment-resistant Depression. If psychedelics turn out to be even partially as effective as they first appear, they could still become the most-effective treatment for depression.
Direct (electrical) treatments
Direct treatments include deep brain stimulation (DBS) and repetitive transcranial magnetic stimulation (rTMS). It is unclear how effective these are compared to other treatments, but we note that NICE do not recommend these as a first-line treatment. Possibly, further research will improve them or demonstrate their potential.
Education and prevention
Of course, we shouldn’t only be thinking about treating people who are already suffering, but also about prevention. One promising (psychological) method of prevention this would be ‘positive education’: teaching resilience and life skills in schools. A series of trials in Bhutan, Peru and Mexico involving over 750,000 students found that positive education not only improved measures of child well-being, but also increased standardised academic test scores.
Mental health vs other life-improving interventions
A large and neglected problem
 A Roth and P Fonagy, What Works for Whom?: A Critical Review of Psychotherapy Research, 2nd ed. (Guilford Publications, 2005).
 Richard Layard and David M. Clark, Thrive : The Power of Evidence-Based Psychological Therapies, n.d.
 Clark, D. M. (2018). “Realizing the Mass Public Benefit of Evidence-Based Psychological Therapies: The IAPT Program,” Annual Review of Clinical Psychology ,14(1), 159–83.
 Layard and Clark, Thrive : The Power of Evidence-Based Psychological Therapies. p143
 B Boecking, “Mechanism of Change in Cognitive Therapy for Social Phobia” (King’s College London, 2010).
 Nicola J Wiles et al. (2016). “Long-Term Effectiveness and Cost-Effectiveness of Cognitive Behavioural Therapy as an Adjunct to Pharmacotherapy for Treatment-Resistant Depression in Primary Care: Follow-up of the CoBalT Randomised Controlled Trial,” The Lancet Psychiatry, 3(2), 137–44.
 Layard and Clark, Thrive : The Power of Evidence-Based Psychological Therapies.
 For a longer discussion of mental health and StrongMinds, see John Halstead and James Snowden, “Cause Report - Mental Health,” n.d.
 Cukrowicz, K. C. and Joiner, T. E. (2007). “Computer-Based Intervention for Anxious and Depressive Symptoms in a Non-Clinical Population.” Cognitive Therapy and Research, 31(5), 677-693.
E Kaltenthaler et al. (2008). “Computerised Cognitive–behavioural Therapy for Depression: Systematic Review.” The British Journal Of Psychiatry, 193(3), 181-184.
 Andrea Cipriani et al. (2018). “Comparative Efficacy and Acceptability of 21 Antidepressant Drugs for the Acute Treatment of Adults with Major Depressive Disorder: A Systematic Review and Network Meta-Analysis.,” The Lancet, 391(10128), 1357–66
Irving Kirsch et al. (2008). “Initial Severity and Antidepressant Benefits: A Meta-Analysis of Data Submitted to the Food and Drug Administration,” PLoS | Medicine, 5(2), e45.
 Keith S. Dobson et al. (2008). “Randomized Trial of Behavioral Activation, Cognitive Therapy, and Antidepressant Medication in the Prevention of Relapse and Recurrence in Major Depression.” Journal of Consulting and Clinical Psychology, 76(3), 468–77.
 O’Leary, O. F., Dinan, T. G. and Cryan, J. F. (2015). “Faster, Better, Stronger: Towards New Antidepressant Therapeutic Strategies,” European Journal of Pharmacology, 753, 32–50.
Marije aan het Rot et al. (2010). “Safety and Efficacy of Repeated-Dose Intravenous Ketamine for Treatment-Resistant Depression.” Biological Psychiatry , 67(2), 139–45.
Rebecca Brachman, Could a Drug Prevent Depression and PTSD? TED Talk, 2016.
 MAPS. (2017). “FDA Grants Breakthrough Therapy Designation for MDMA-Assisted Psychotherapy for PTSD, Agrees on Special Protocol Assessment for Phase 3 Trials.”
Michael C Mithoefer et al. (2013). “Durability of Improvement in Post-Traumatic Stress Disorder Symptoms and Absence of Harmful Effects or Drug Dependency after 3,4-Methylenedioxymethamphetamine-Assisted Psychotherapy: A Prospective Long-Term Follow-up Study.” Journal of Psychopharmacology, 27(1), 28–39.
 Robin L Carhart-Harris et al. (2016). “Psilocybin with Psychological Support for Treatment-Resistant Depression: An Open-Label Feasibility Study,” The Lancet Psychiatry, 3(7), 619–27.
See also: Nichols, D. E. , Johnson, M. W. and Nichols, C. D. (2017). “Psychedelics as Medicines: An Emerging New Paradigm,” Clinical Pharmacology and Therapeutics, 101(2), 209-219.
 Plant, M. and Sharkey, L. (2017). “High Time For Drug Policy Reform. Part 1/4: Introduction and Cause Summary.” Effective Altruism Forum.
 Sidney H. Kennedy et al. (2011). “Deep Brain Stimulation for Treatment-Resistant Depression: Follow-Up After 3 to 6 Years.” American Journal of Psychiatry, 168(5), 502–10.
 J Brunelin et al. (2007). “Efficacy of Repetitive Transcranial Magnetic Stimulation (RTMS) in Major Depression: A Review.” L’Encephale, 33(2), 126–34.
 Alejandro Adler, (2016). “Teaching Well-Being Increases Academic Performance: Evidence From Bhutan, Mexico, and Peru.” Publicly Accessible Penn Dissertations.