Aspirin was around in 1915, but probably wasn't very widely known. The tablet form we know and love had just been developed. From "The History of Aspirin:"

By 1829, scientists discovered that it was the compound called salicin in willow plants which gave you the pain relief.

The problem was that salicylic acid was tough on stomachs and a means of 'buffering' the compound was searched for. The first person to do so was a French chemist named Charles Frederic Gerhardt. In 1853, Gerhardt neutralized salicylic acid by buffering it with sodium (sodium salicylate) and acetyl chloride, creating acetylsalicylic acid. Gerhardt's product worked but he had no desire to market it and abandoned his discovery.

In 1899, a German chemist named Felix Hoffmann, who worked for a German company called Bayer, rediscovered Gerhardt's formula. Felix Hoffmann made some of the formula and gave it to his father who was suffering from the pain of arthritis. With good results, Felix Hoffmann then convinced Bayer to market the new wonder drug. Aspirin was patented on February 27, 1900.

Aspirin was first sold as a powder. In 1915, the first Aspirin tablets were made. Interestingly, Aspirin ® and Heroin ® were once trademarks belonging to Bayer. After Germany lost World War I, Bayer was forced to give up both trademarks as part of the Treaty of Versailles in 1919.