Morphine is the most important pharmacologically active ingredient in opium, the resin obtained from the dried juice of the opium poppy. More than 200 years ago, morphine first appeared in clinical practice. This is the first model of opioid medicine, whose analgesic and satisfying effects are mediated by the activation of opioid receptors which are obtained mainly in the central nervous system (CNS). The World Health Organization (WHO) has proposed that morphine continues to be the potent opioid of choice for treating patients with moderate to severe cancer pain. Pharmacology Endorphins, enkephalins and dynorphins are endogenous opioids. Morphine mimics endorphins which are responsible for reducing pain, producing drowsiness and feelings of pleasure. Morphine is a sample narcotic drug and is the standard against which all other opioids are examined. It interacts mainly with the µ-opioid receptor. These places of combination of µ are discreetly dispersed in the brain and in certain cortical areas. They are also located on the axon terminals of primary afferents in lamina I and II of the spinal cord and in the spinal nucleus of the trigeminal nerve. Morphine is a phenanthrene alkaloid opioid receptor agonist. ''It is a weak base with a PKa of 7.9 at physiological PH, 76% of its molecules are ionized'' and it is comparatively water-soluble and poorly lipid-soluble. The main effect of morphine is to comb and activate μ-opioid receptors in the CNS. The basic pharmacological effect of morphine applies in the clinical setting on the (CNS) and gastrointestinal tract (GIT). Its therapeutic effect has two main actions which are analgesia and sedation. Morphine is also an agonist at the κ and δ-opioid receptors, the action of κ-opioids...... middle of article ...... weak onset of action than NR modulations. There are twice-daily preparations with an initial action of 1-2 hours and reaching the maximum intensity of the drug after 4 hours. The once-daily MR preparation has a slower initial action and reaches peak levels at 8.5 hours. The many beneficial effects of morphine are due to reduced pain perception, decreased pain response, and increased pain tolerance. In contrast, the most widely recognized side effects are sedation, respiratory depression and constipation as well as nausea and vomiting, while there are other common ones such as tolerance, physical and psychological dependence. All these adverse effects of morphine can be reduced by five possible methods: decreasing the dose, changing the route of administration and using certain adjuvant medications as well as opioid rotation and symptomatic management of adverse effects..