originally a brand name, aspirin is now a generic term for acetylsalicylic acid (C 9 H 8 O 4 ), a common over the counter non-steroidal anti-inflammatory Side effects include inhibition of blood clotting (so that it may increase internal bleeding and/or the extent of bruising if used when an injury is fresh). acetaminophen (Tylenol®) may be used when a pain killer without these effects is desired, though it will not provide any anti-inflammatory effects, nor may it be substituted for aspirin in the ECA stack.