In approximately 400BC, Hippocrates discovered that chewing on the bark of willow trees helped women overcome the pain associated with childbirth. The active ingredient in the plant, salicylic acid, was later extracted and isolated. Modern aspirin is a derivative compound, with an acetyl group added to reduce the original substance's irritant effect on the digestive system.
As aspirin has a thinning effect on the blood. It reduces blood pressure (hypotension), resulting in decreased oxygen perfusion of the brain. This creates the risk of loss of consciousness and brain damage. Caution should be used when being tattooed or pierced while taking aspirin for pain relief, or when subsequently taking aspirin to relieve post-procedural pain. Excessive bleeding may result. For this reason, a significant number of studios will not perform a procedure on an individual who has taken aspirin in the last 24 hours.
Analgesics which do not significantly thin the blood (and are therefore safer in conjunction with modification) include acetaminophen/paracetamol (sold as Tylenol in the US), ibuprofen (Advil), naproxen sodium (Aleve) and other NSAIDs (Non-Steroidal Anti-Inflammatory Drug).