Medical Astrology
The Tradition that Linked the Sky, the Body and the Temperaments
Medical astrology, once known as iatromathematics, is one of the oldest applications of astrology. For centuries, physicians such as Hippocrates, Galen and Nicholas Culpeper connected the signs of the zodiac, the planets and the bodily humours in order to understand a person's temperament and the course of an illness. The famous saying attributed to Hippocrates — that a physician without knowledge of astrology has no right to call himself a physician — shows how central this art once was to medicine. It is essential to understand this guide for what it is: a historical and cultural presentation of a tradition, written for purely educational purposes. Medical astrology is not a science and makes no diagnosis. It is in no way a substitute for modern medicine. For any health matter, only a doctor or qualified healthcare professional can examine, diagnose and treat you.
Key Concepts
Melothesia
Each sign of the zodiac rules a region of the body, from Aries (the head) down to Pisces (the feet). It is the symbolic map linking the sky to anatomy.
The Four Humours
Blood, phlegm, yellow bile and black bile: the balance of these humours was said to define health and temperament — sanguine, phlegmatic, choleric or melancholic.
Planetary Significators
Each planet rules organs and functions: the Sun the heart and vitality, the Moon the fluids, Mars inflammation, Saturn the bones and structures.
The Houses of Health
The 1st house describes the body and vitality, the 6th illness and daily regimen, the 8th crises, and the 12th exhaustion and convalescence.
The Decumbiture Chart
The chart cast for the exact moment a person falls ill or takes to their bed, traditionally used to judge the likely course of the condition.
The Moon and Critical Days
The Moon's swift motion was used to identify the 'critical days', turning points at which the patient's condition was thought to shift.
What Is Medical Astrology?
Medical astrology is the traditional branch of astrology that draws correspondences between the heavens and the human body. In this worldview, inherited from antiquity, the microcosm (the human being) mirrors the macrocosm (the universe): signs, planets and their configurations are associated with parts of the body, organs, temperaments and imbalances.
In practice, the traditional astrologer examined the birth chart to describe a person's 'constitution' — their make-up, their points of fragility, their dominant temperament — and could then cast occasional charts, such as the decumbiture, to follow a declared illness. It must be stated plainly: these practices belong to a symbolic and historical tradition with no scientific validity. They illuminate the history of medicine and of ideas, but they neither diagnose nor treat anything.
A Tradition from Hippocrates to Culpeper
The roots of medical astrology reach back to Mesopotamia and Egypt, but it was Greek medicine that gave it its lasting form. Hippocrates (5th century BC) and later Galen built the theory of the four humours, tied to the four elements and to the qualities hot/cold and dry/moist.
In the Middle Ages and the Renaissance, medical astrology became a pillar of physicians' training in Europe. Ephemerides were consulted before a bloodletting or the administration of a remedy. In the 17th century, the Englishman Nicholas Culpeper popularised the art in his herbal, assigning each plant to a planet and a sign. The rise of experimental medicine, anatomy and modern biology later removed these ideas from the medical field; today they belong to cultural history and to traditional astrology.
Melothesia: the Zodiac and the Body
Melothesia is the doctrine that assigns each sign of the zodiac to a part of the body, in a descending order from head to feet. Aries rules the head and face; Taurus the throat and neck; Gemini the shoulders, arms and lungs; Cancer the chest and stomach; Leo the heart and back; Virgo the abdomen and intestines.
Libra governs the kidneys and lower back; Scorpio the genitals and elimination; Sagittarius the hips and thighs; Capricorn the knees, skin and bones; Aquarius the legs and circulation; Pisces the feet and lymphatic system. The 'zodiac man' (homo signorum), engraved in countless medieval manuscripts, illustrates this symbolic map of the body linked to the sky.
The Four Humours and the Temperaments
At the heart of ancient medicine lies the theory of the humours. Four bodily fluids are associated with the four elements: blood (air, hot and moist), phlegm (water, cold and moist), yellow bile (fire, hot and dry) and black bile (earth, cold and dry).
The balance among these humours was thought to determine both health and personality, yielding the four temperaments: sanguine (sociable, optimistic), phlegmatic (calm, steady), choleric (energetic, irritable) and melancholic (thoughtful, prone to sadness). From the birth chart — through the dominant elements, the sign and the phase of the Moon — the astrologer read the person's underlying temperament. This framework deeply marked Western culture, far beyond medicine, down to everyday language.
The Planets, the Organs and the Functions
In the tradition, each planet rules organs, tissues and vital functions. The Sun governs the heart, vitality and life force; the Moon the fluids, the stomach and the body's rhythms; Mercury the nervous system, the breath and coordination.
Venus is linked to the kidneys, the throat and hormonal harmony; Mars to heat, inflammation, the muscles and the blood; Jupiter to the liver, growth and abundance; Saturn to the bones, teeth, skin and processes of hardening or slowing. Astrologers also read the state of a planet — its strength, its difficult aspects, its placement in the 6th house — as a symbolic indication of the matching bodily function. Here again, these are symbolic correspondences, not physiological facts.
The Houses of Health
The system of twelve houses gave the traditional astrologer a reading of life's domains, several of which concern health. The 1st house, and its rising sign, describes the physical body, the constitution and general vitality. The 6th house is par excellence that of illness, daily regimen, work and care.
The 8th house touches on crises, deep transformations and, symbolically, situations where life is at stake. The 12th house evokes exhaustion, hospitalisation, convalescence and all that unfolds out of sight. By examining the rulers of these houses and the planets within them, the astrologer drew a portrait of the 'constitution'. Remember that this reading is interpretive and can never replace a clinical examination.
The Decumbiture Chart
The decumbiture (from the Latin decumbere, 'to lie down') is the chart cast for the precise moment a person falls ill or takes to their bed. Close to the horary chart, it was used to judge the nature of the illness, its probable severity and its course.
The astrologer examined the Ascendant and its ruler for the patient, the 6th house for the illness, and above all the Moon, whose successive aspects symbolically told the story of the condition. The Moon's position relative to where it stood at the onset served to identify the critical days. Beautifully documented in authors such as Culpeper, this method illustrates the formal rigour of the tradition — yet it remains a symbolic exercise, never a reliable tool of medical prognosis.
The Moon, Critical Days and Timing
No celestial body holds a place as central as the Moon in medical astrology. Through its swift course across the zodiac — about twelve to thirteen degrees per day — it served as the hand on the symbolic clock of the body and of illness.
Astrologer-physicians watched the lunar phase, the sign the Moon was crossing (in connection with melothesia) and its aspects to the other planets. From these they inferred 'critical days', moments when the patient's condition was expected to turn, as well as periods judged favourable or unfavourable for giving a remedy. Many, for example, avoided operating on a part of the body while the Moon crossed the sign that rules it. These beliefs belong to the history of medicine and have no operative value today.
The Constitution: Indications in the Birth Chart
Even before any illness, traditional astrology read in the birth chart what it called the 'constitution': overall robustness, dominant temperament and the symbolically more sensitive zones of the body. It looked above all at the Ascendant and its ruler, the Sun and the Moon (the 'luminaries', guardians of vitality) and the 6th house.
A strongly dominant or deficient element, a difficult planet on the Ascendant, or a cluster of bodies in the 6th house were read as signs of underlying tendencies. The aim was not to predict a specific illness but to describe a temperamental predisposition. This approach keeps a reflective and cultural value, provided it is never confused with screening or a real medical assessment.
Medical Astrology Today
Contemporary medical astrology has abandoned any claim to diagnosis. Serious practitioners treat it as a symbolic language oriented towards self-knowledge: exploring one's temperament, rhythms, and relationship to the body, to stress and to rest, much like a tool of psychological or contemplative reflection.
In this perspective, sometimes likened to a psychosomatic reading, the chart becomes a support for inner dialogue, never a substitute for medical care. A responsible astrologer offers no remedy, never advises against treatment, and systematically refers people to a doctor as soon as a concrete health question arises. It is precisely this caution that distinguishes an ethical approach from a potentially dangerous practice.
Limits, Caution and Medical Advice
This point is the most important in the whole guide. Medical astrology is a symbolic and historical tradition: it has no demonstrated diagnostic, predictive or therapeutic value. No birth chart can detect, confirm or rule out an illness, nor indicate a treatment.
Never make a health decision on the basis of an astrological chart. Do not change, interrupt or refuse a treatment, an examination or medical follow-up because of an astrological interpretation. If you feel a symptom, pain, or concern for your physical or mental health, consult a doctor, a pharmacist or a qualified healthcare professional — and in an emergency, call the emergency services without delay. Approach medical astrology as an object of culture and curiosity, and entrust your health to medicine.