Here's some info from eCureme.
Aspirin is a common over-the-counter pain/fever reducer. Aspirin is also found in combination with some over-the-counter and prescription medications, such as Excedrin, Anacin, Fiorinal, and Percodan.
Aspirin taken at higher-than-recommended doses can cause severe toxicity. At a biochemical level, aspirin interferes with the normal energy-producing pathways (aerobic metabolism). This results in the body using a different pathway (anaerobic metabolism) -- creating excessive Lactic acid and heat.
Aspirin also causes inflammation of the stomach lining and Gastritis or bleeding ulcers. Aspirin overdose can occur by taking a large amount at one time, or by taking lower doses over a continuous period
Symptoms:
Nausea/vomiting
Rapid breathing
Heart racing
Ringing in ears
Agitation
Confusion
Seizures
Coma