See also Warning section. Nausea, drowsiness, dizziness, trouble sleeping, loss of appetite, weakness, tiredness, dry mouth, sweating, yawning, or headache may occur. If any of these effects persist or worsen, tell your doctor promptly. Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects. Tell your doctor immediately if any of these unlikely but serious side effects occur: unusual or severe mental/mood changes (e.g., agitation, thoughts of suicide), shakiness (tremor), restlessness, inability to keep still, decreased interest in sex, changes in sexual ability, blurred vision, numbness/tingling. Tell your doctor immediately if any of these rare but very serious side effects occur: bloody/black/tarry stools, vomit that looks like coffee grounds, easy bruising/bleeding, fainting, fast/irregular heartbeat, muscle weakness/spasm, seizures, change in amount of urine. This medication may rarely cause a very serious condition called serotonin syndrome. The risk increases when this medication is used with certain other drugs such as "triptans" used to treat migraine headaches (e.g., sumatriptan, eletriptan), certain antidepressants including other SSRIs (e.g., citalopram, fluoxetine) and SNRIs (e.g., duloxetine, venlafaxine), lithium, tramadol, tryptophan, or a certain drug to treat obesity (sibutramine). Before taking this drug, tell your doctor if you take any of these medications. Serotonin syndrome may be more likely when you start or increase the dose of any of these medications. Seek immediate medical attention if you develop some of the following symptoms: hallucinations, unusual restlessness, loss of coordination, fast heartbeat, severe dizziness, unexplained fever, severe nausea/vomiting/diarrhea, twitchy muscles. For males, in the very unlikely event you have a painful or prolonged erection lasting 4 or more hours, stop using this drug and seek immediate medical attention, or permanent problems could occur. A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing. This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist. In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088. In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.