As with all drugs that alter haemostasis, aspirin can be associated with bleeding.

It is contraindicated in patients with active bleeding (e.g. peptic ulcer disease, intracranial haemorrhage) and should be used with caution in patients with risk factors that increase their risk of bleeding, such as:

• ≥75 years
• History of bleeding
• Recent trauma/surgery
• Liver disease (clotting factors are made in the liver)
• Concomitant use of NSAIDs or anticoagulants
• Bleeding disorders

Patients may experience minor or major bleeding.

• Clopidogrel is a prodrug and is converted into its active form in the liver the superfamily of cytochrome P450 enzymes.
• Omeprazole (a proton pump inhibitor) impairs the function of the CYP2C19 enzyme, which is involved in the activation of clopidogrel. So, the effects of clopidogrel may be reduced in patients also taking omeprazole.