Tea contains two other alkaloids, theobromine and theophylline in addition to caffeine.
These first two relax the smooth muscles where caffeine stimulates the heart and nervous and respiratory systems. In the past aspirin was combined with phenacetin and caffeine as a painkiller, but these days most headache preparations don't contain caffeine at all. No Doze and Dynamo each have 100mg of caffeine per tablet. Caffeine is present in coffee beans to a maximum of 4 per cent. Most varieties have less than this, and the degree of roasting will slightly alter the content.