1Fentanyl is a powerful synthetic opiate analgesic, which has a primary function in the management of malignant and non-malignant contracting pain, similar to morphine, but is more powerful. Indeed, fentanyl has an octanol-water partition of 9,550, compared to morphine, which has 6. This effectively demonstrates that fentanyl is highly lipid soluble and crosses the blood-brain barrier more quickly. Therefore, its reaction time is faster but shorter in duration than morphine. It is commonly used to treat patients with severe pain or patients with pain after surgery. Fentanyl may also be used to treat chronic pain patients who are physically tolerant to opioids. Patients who cannot physically tolerate opioids should avoid using fentanyl because it can cause unwanted side effects, which in some cases can be toxic. Fentanyl is registered as a Class II prescription drug, meaning it has a greater risk of abuse, which could have negative implications on the patient's health, as it can lead to psychological or physical dependence .12Fentanyl binds to the mu opioid receptor in the central nervous system, reducing the perception of pain but also the emotional response to pain. When the fentanyl patch is applied to the skin, a concentration gradient develops, which allows the fentanyl molecules to diffuse down the concentration gradient. A second drug reservoir will then be established in the striatum corneum, allowing absorption into the local capillary vasculature, followed subsequently by delivery into the systemic circulation. Drug transport across the skin can occur through the hair follicle and sweat ducts, but the primary and targeted pathway is passive diffusion, movement...... middle of paper ...... side effects such as analgesia, altered mood and drowsiness may occur. Fentanyl depresses the respiratory centers and cough reflexes in addition to constricting the pupils. The analgesic blood concentration of fentanyl can cause nausea and vomiting due to stimulation of the chemoreceptor trigger zone.55 Opioids increase tone and decrease smooth muscle contractions of the gastrointestinal tract. The transit time caused by fentanyl may be responsible for its constipating effect. Due to increased bile duct pressure, some patients may experience worsening pain rather than pain relief. Fentanyl can cause orthostatic hypotension and fainting.55 Overall, fentanyl matrix patches are found to be safe and effective only for opioid-tolerant patients, and have minimal adverse effects, the most common being nausea and nausea. reactions at the application site..