Why are Blood Thinners prescribed?

• Pulmonary Embolism (PE) or Pulmonary thromboembolism (PTE) (27%)
• Atrial Fibrillation (AFib) (26%)
• Deep Vein Thrombosis (DVT) (24%)
• Heart Attack (19%)
• Stroke Risk Reduction (5%)
• Other (1%)
• Those who've had hip or knee replacement surgery.

Blood thinners can increase the chance of intracerebral (brain) bleeding or bleeding from a peptic ulser.

Blood Thinners work in different ways.
Antiplatelet agents: (asparin, clopidogrel, prasugrel, or ticagrelor) are P2Y12 Receptor Antagonist. They keep the platelets from sticking together.
Plavix (clopidogrel) Brilinta (ticagrelor)

Anticoagulants:
Warfarin [Coumadin], the old standby reduces your liver's ability to use vitamin K to make these blood clotting proteins, which makes it harder for your blood to clot.

The new drugs 2011-
Sometimes referred to as Novel Oral Anticoagulant (NOAC)

Doctors prescribe newer drugs over warfarin for several reasons. First, they require no regular patient monitoring or blood tests. (Warfarin requires at least one blood test and doctor's visit each month to check its efficacy.) Doctors also like that the newer anticoagulants were designed to avoid warfarin's risks, including brain hemorrhages and other dangerous bleeding events. Unlike warfarin, the newer blood thinners don't require any dietary or lifestyle changes, which appeals to doctors and patients alike.

If not prescribed properly, these new drugs can cause even more serious problems than warfarin. Worryingly, the side effects are just as extreme.

Factor Xa inhibitors (apixaban [Eliquis], rivaroxaban [Xarelto], and Edoxaban [Savaysa]) work by selectively and reversibly blocking the activity of clotting factor Xa, preventing clot formation.

Thrombin Inhibitors:
Heparin also works by preventing certain cofactors, namely thrombin and fibrin, from working correctly. Heprin is injected and sometimes used during surgery.

Pradaxa [Dabigitran] is a direct thrombin inhibitor

Compare Pradaxa vs Heparin .
Direct thrombin inhibitors | ncbi.nlm.nih.gov

Bleeding:
About one in six people who take an anticoagulant will experience some kind of internal bleeding, for example in their stomach, intestines, or urinary tract. And about 3 percent of people who take an anticoagulant will have a major bleeding episode, including those in the brain that, if not treated immediately, could be fatal.

Bleeding is less of a risk with the new medications. And since they wear off faster than warfarin, bleeding problems may not be as serious when they happen.
However, there is an "antidote" for warfrin to reverse it's effects immediately.
As of 2017 there was no antidote for the new drugs.
If an emergency bleed occurs while taking Xarelto or Eliquis, there's no way to reverse anticoagulation and clot the blood. In other words, severe bleeding events can be fatal.

Other Issues:
Coumadin- Requires International normalized ratio (INR) testing, via blood tests, every 4 weeks.
Vitamin K, primarily found in leafy green vegetables such as spinach, broccoli, lettuce, and some vegetable oils can alter the metabolism of warfarin (Coumadin^®).
Side effects include:

• Easy bruising and minor bleeding
• May cause serious bleeding if it affects blood-clotting proteins too much
• Unusual pain/swelling/discomfort
• Prolonged bleeding from cuts or gums
• Heavy/prolonged menstrual flow
• Severe headache
• Dizziness/fainting