Tell your doctor immediately if any of these rare but very serious side effects occur:
- stomach/abdominal pain
- chest pain
- persistent cough
- shortness of breath
- bloody/black/tarry stools
- vomit that looks like coffee grounds
- easy bruising/bleeding
- fast/irregular/pounding heartbeat
- muscle weakness/cramps
- yellowing eyes/skin
- dark urine
- seizures
- unusual tiredness
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 SSRIs (e.g., citalopram, paroxetine) and other SNRIs (e.g., duloxetine), lithium, tramadol, tryptophan, or a certain drug to treat obesity (sibutramine). See also Drug Interactions section. 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
- fainting
- 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.
Call your doctor for medical advice about side effects. In the US, you may report side effects to the Food and Drug Administration (FDA) at 1-800-FDA-1088.
In Canada, you may report side effects to Health Canada at 1-866-234-2345.
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