Friend had a blood clot in lung. he is fine now but is on blood thinners. will this be needed life long? what can cause? nothing mentioned.

Depending : Depends on many things. Young patients with blood clots and/or family history of blood clots need to be screened for hereditary causes. Also doctors look for provoking factors such as long car trips, recent surgery, cancer. The above info is used to make a decision if lifelong anti coagulation is needed...

Anticoagulation: The source of the blood clot to the lungs is usually the veins in the legs in 90% of patients. Usual length of time for blood thinners is 3-6 months. However, if there is more than one episode of blood clots, or if your friend has a genetic predisposition to forming blood clots, the blood thinners may be recommended lifelong. Your friend should followup with a vascular specialist or primary car.

Several reasons: Blood clots are divided into provoked and unprovoked. Provoked blood clots have a determined cause (such as recent surgery, long period of immobility, known blood clotting disorder, certain medications, etc.). The circumstances in which the blood clot occured will determine the length of time someone needs to be on a blood thinner.