Codeine is a medication used to manage mild to moderate pain. This medication is typically combined with other medications to treat coughing, according to MedlinePlus 2. Codeine belongs to medications called opiate (narcotic) analgesics and antitussives. This medication alters your perception of pain and reduces coughing by affecting a certain area in your brain. Codeine is available as a pill and you should take it as your doctor prescribes. If you are experiencing serious medical symptoms, seek emergency treatment immediately. Common Side Effects According to Drugs.com, codeine's most common side effects include:- drowsiness 1Vomiting results in a reduction of bodily fluid and dehydration and low blood potassium levels. Manifestations of dehydration include dry skin and decreased urination. Drink seven to 10 cups of water a day to replace your lost fluids. Signs of low potassium include constipation and muscle spasms. Add apricots, bananas and other potassium-rich foods to your meals to elevate your potassium levels. Codeine can also cause blurry vision, a skin rash, headache and loss of sex drive (libido). Inform your doctor when codeine's common manifestations last for more than a week. Serious Side EffectsMedlinePlus says that codeine's serious side effects include trouble breathing, difficulty swallowing (dysphagia) and seizures 2. Choking can occur when you have trouble swallowing. Seizures occur when the electrical activity in your brain is very high. Prolonged seizures lasting for more than 30 minutes is potentially fatal and can result in brain damage or death. Codeine can also cause a fast heartbeat (tachycardia), an irregular heartbeat (arrythmia) and a pounding heartbeat (palpitations). Changes in your heartbeat affect the amount of blood flow through your body. Chest pain can result when less blood goes to your heart and a severe headache can happen when your brain doesn't receive enough blood. Phone your doctor immediately when codeine causes these side effects. Avoid codeine if you are hypersensitive to opiate analgesics or antitussive medications. A hypersensitivity reaction to codeine includes throat or tongue swelling, hives and difficulty breathing. Do not use codeine if you have a history of drug or substance abuse. You may become psychologically and physically addicted to codeine. You should not combine it with alcohol because this can lead to death. Codeine is excreted into breast milk, so tell your physician if you are nursing. Codeine is a medication used to manage mild to moderate pain. This medication alters your perception of pain and reduces coughing by affecting a certain area in your brain. Codeine is available as a pill and you should take it as your doctor prescribes. Codeine can also cause blurry vision, a skin rash, headache and loss of sex drive . MedlinePlus says that codeine's serious side effects include trouble breathing, difficulty swallowing and seizures. Do not use codeine if you have a history of drug or substance abuse.- Jupiterimages/Polka Dot/Getty Images