Codeine phosphate is a constituent of opium and was discovered to have similar properties to morphine with the additional benefit of being less addictive. The French Chemist Pierre-Jean Robiquet was the first person to extract codeine from opium in 1832, hence the use of the collective terms "opiates" or "opioids" to describe these narcotics. Codeine can either be obtained in this way, extracted from the opium poppy (Papaver Somniferum), or through the methylation of morphine. After extraction, codeine would only constitute approximately 0.5% of raw opium. Because of the small concentration of codeine found in the opium poppy, almost all the codeine found in modern medical products is synthesised from morphine.Codeine is a phenanthrentic, or piperidinophenantrene, alkaloid of opium. It belongs to a class of medications known as narcotic analgesics, which are used in cases of moderate to severe pain relief. Codeine is also used as a cough suppressant and has been used as a sedative and antispasmodic. In the nineteenth century, codeine was even used as an antidepressant.Codeine is a weak opiate agonist that provides relief from pain by blocking the pain signals that are being sent from the brain to affected areas of the body. Within half an hour it works on the Central Nervous System (CNS) to inhibit these pain signals. Because the transmission of the pain signals has been impaired, less pain is felt, even if the original source of the pain remains. In this regard, codeine mimics the effects of endorphins, which are naturally occurring painkilling chemicals produced by the body.While achieving this, codeine does not alter the pain threshold of afferent nerve endings in response to noxious stimuli or change the way impulses are transferred along peripheral nerves. An analgesia affect occurs when codeine binds with stereospecific receptors at various sites in the CNS causing alterations in the processes involving the perception of pain and the emotional response to pain. Common forms of pain that codeine is used to treat include back pain and lumbago, arthralgia and neuralgic nerve pain, bone pain, arthritic pain, fibrosis, myalgia and rheumatic muscular pain, dental pain, headache, migraine, surgical pain, period and cramping pain.To experience the painkilling properties of codeine the body must first convert it into morphine. Codeine is readily absorbed by the gastrointestinal tract, becoming quickly transported to various tissues throughout the body. Codeine does not accumulate in body tissues because it is metabolised by the liver and its metabolic products are excreted by the kidneys. The process by which codeine is metabolised is known as glucuronidation. Through O-demethylation the codeine is converted into morphine and through N-demethylation it becomes norcodeine. The metabolism rate is approximately 30 mg of codeine in an hour and about 90% of the drug will be excreted from the body within a day. In most people, only about 10% of codeine is transformed into morphine. The antitussive and analgesic attributes of codeine also enable it to work as a cough suppressant, especially with dry, non-productive coughs. It does this by inhibiting the receptor in the cough centre of the medulla oblongata and acting on the brain to reduce the cough reflex, without the suppression of the respiratory centre. Codeine increases the viscosity of bronchial secretions and has a drying effect on the respiratory tract.Codeine is used in many medicines all around the world, usually in the form of phosphate salts or sulphate. Codeine phosphate is available in products in a combination with aspirin, paracetamol, ibuprofen or doxylamine succinate. Most modern medicines are formulated in a way that makes it very difficult to separate the codeine from the other components, thereby reducing the risk of the codeine being extracted for illegal purposes.