What are the mental health standards (if any) that a candidate pilot must meet in order to qualify for a medical certificate?
Answers for Canada, the US, and Europe would be particularly interesting to me.
1.3 The applicant shall have no established medical history or clinical diagnosis which, according to accredited medical conclusion, would render the applicant unable to exercise safely the privileges of the permit, licence or rating applied for or held, as follows: (a) psychosis or established neurosis; (b) alcohol or chemical dependence or abuse; (c) a personality or behaviour disorder that has resulted in the commission of an overt act; (d) other significant mental abnormality
Unless otherwise directed by the FAA, the Examiner must deny or defer if the applicant has a history of: [...] (8) Psychosis; (9) Bipolar disorder; (10) Personality disorder that is severe enough to have repeatedly manifested itself by overt acts; (11) Substance dependence; (12) Substance abuse; [...]
EASA (Europe) (abbreviated):
AMC1 MED.B.055 Psychiatry (a) Psychotic disorder (b) Organic mental disorder (c) Psychotropic substances (d) Schizophrenia, schizotypal or delusional disorder (e) Mood disorder (f) Neurotic, stress-related or somatoform disorder (g) Personality or behavioural disorder (h) Disorders due to alcohol or other substance use (i) Deliberate self-harm
AMC1 MED.B.060 Psychology (a) Where there is suspicion or established evidence that an applicant has a psychological disorder, the applicant should be referred for psychological opinion and advice. (b) Established evidence should be verifiable information from an identifiable source which evokes doubts concerning the mental fitness or personality of a particular individual. Sources for this information can be accidents or incidents, problems in training or (c) The psychological evaluation may include a collection of biographical data, the administration of aptitude as well as personality tests and psychological interview.
(d) The psychologist should submit a written report to the AME, AeMC or licensing authority as appropriate, detailing his/her opinion and recommendation.
The US Medical Certificate application form (FAA 8500-8, the thing we fill out online now) includes a question asking if you have or have ever been diagnosed with
Mental disorders of any sort; depression, anxiety, etc.
If you answer yes your application for a medical is subject to additional scrutiny, and per the FAA's guidance:
An applicant with an established history of a personality disorder that is severe enough to have repeatedly manifested itself by overt acts, a psychosis disorder, or a bipolar disorder must be denied or deferred by the Examiner.
For further reading you can find references to the relevant regulations, examination techniques, and guidance on dispositions (Issue, Defer, or Deny the application) in the FAA's Guide for Aviation Medical Examiners, and in FARs 61.107, 61.207, and 61.307 (for the first, second, and third class medical standards, respectively).