(Christianity)
The four holy cities of Judaism: Jerusalem, Hebron, Safed, and Tiberius

Hinduism
There are four Vedas: Rigveda, Samaveda, Yajurveda and Atharvaveda. In Puruṣārtha, there are four aims of human life: Dharma, Artha, Kāma, Moksha. The four stages of life Brahmacharya (student life), Grihastha (household life), Vanaprastha (retired life) and Sannyasa (renunciation). The four primary castes or strata of society: Brahmana (priest/teacher), Kshatriya (warrior/politician), Vaishya (landowner/entrepreneur) and Shudra (servant/manual laborer). The swastika symbol is traditionally used in Hindu religions as a sign of good luck and signifies good from all four directions. The god Brahma has four faces. There are four yugas: Satya, Dvapara, Treta and Kali

Islam
Eid al-Adha lasts for four days, from the 10th to the 14th of Dhul Hijja. The four holy cities of Islam: Mecca, Medina, Jerusalem and Damascus. The four tombs in the Green Dome: Muhammad, Abu Bakr, Umar ibn Khattab and Isa ibn Maryam (Jesus). There are four Rashidun or Rightly Guided Caliphs: Abu Bakr, Umar ibn al-Khattab, Uthman ibn Affan and Ali ibn Abi Talib. The Four Arch Angels in Islam are: Jibraeel (Gabriel), Mikaeel (Michael), Izraeel (Azrael), and Israfil (Raphael)
There are four months in which war is not permitted: Muharram, Rajab, Dhu al-Qidah and Dhu al-Hijjah. There are four Sunni schools of fiqh: Hanafi, Shafi`i, Maliki and Hanbali. There are four major Sunni Imams: Abū Ḥanīfa, Muhammad ibn Idris ash-Shafi`i, Malik ibn Anas and Ahmad ibn Hanbal. There are four books in Islam: Taurait, Zaboor, Injeel, Quran.
Side effects
Sodium and water retention
Swelling due to fluid retention (edema)
High blood pressure (hypertension)
Headache
Low blood potassium level (hypokalemia)
Muscle weakness
Fatigue
Increased susceptibility to infection
Impaired wound healing
Increased sweating
Increased hair growth (hirsutism)
Thinning of skin and stretch marks
Disturbances of the gut such as indigestion (dyspepsia), distention of the abdomen and ulceration (peptic ulcer)
Decreased bone density and increased risk of fractures of the bones
Difficulty in sleeping (insomnia)
Depression
Weight gain
Raised blood sugar level
Changes to the menstrual cycle
Partial loss of vision due to opacity in the lens of the eye (cataracts)
Raised pressure in the eye (glaucoma)
Increased pressure in the skull (intracranial pressure)

Pharmacology
Fludrocortisone is a corticosteroid and acts as a powerful mineralocorticoid, along with some additional but comparatively very weak glucocorticoid activity. Relative to cortisol, it is said to have 10 times the glucocorticoid potency but 250 to 800 times the mineralocorticoid potency. Fludrocortisone acetate is a prodrug of fludrocortisone, which is the active form of the drug.Plasma renin, sodium, and potassium are checked through blood tests to verify that the correct dosage is reached. Chemistry
Fludrocortisone, also known as 9α-fluorocortisol (9α-fluorohydrocortisone) or as 9α-fluoro-11β,17α,21-trihydroxypregn-4-ene-3,20-dione, is a synthetic pregnane steroid and a halogenated derivative of cortisol (11β,17α,21-trihydroxypregn-4-ene-3,20-dione). Specifically, it is a modification of cortisol with a fluorine atom substituted in place of one hydrogen atom at the C9α position. Fluorine is a good bioisostere for hydrogen because it is similar in size, with the major difference being in its electronegativity. The acetate form of fludrocortisone, fludrocortisone acetate, is the C21 acetate ester of fludrocortisone, and is hydrolyzed into fludrocortisone in the body.