Hooker criticized the use of drugs and advocated exercise, fresh air and a vegetarian diet.

[2] Hook was a Vice-President of the naturopathic Psycho-Therapeutic Society which was founded in 1901 for the "Study, Investigation, and Practice of Health Reform, Medical Hypnosis, Suggestive Therapeutics, Curative Human Radiations, and Drugless Healing, with due regard to Diet, Hygiene, and the observance of Natural Laws of Health".

[2] Hooker stated that mind over matter had a "tremendous power" and predicted that the work of the Psycho-Therapeutic Society "would undoubtedly develop in view of increase in nervous disease".

[3] Hooker and his wife joined the British Nature Cure Association in 1907 and were on its executive committee.

[2] In 1925, he was brought before the General Medical Council and was found "guilty of infamous conduct in a professional respect" for promoting an alleged "consumption cure" known as Newell treatment that was published in the John Bull magazine.

[15][16] In 1907, thirteen medical men including Hooker signed a manifesto stating that vegetarianism is "scientifically a sound and satisfactory system of dietetics" and superior to health than meat eating.

[18] He held the view that all organisms emit N-rays and they are coloured differently depending on mental and physical factors of the individual.