 Zelmid was a selective serotonin reuptake inhibitor (SSRI), and although Astra was a pioneer in the SSRI area, they did not follow up with another drug using the same mechanism.Instead, it was the US pharmaceutical company Eli Lilly and Company which later introduced the bestselling SSRI drug Prozac, which led Astra to realise that they would probably had been able to beat Lilly to this lucrative market if they had continued their SSRI drug development.Despite losing out in the SSRI area, in the 1990s, Astra had become one of the heaviest companies on the Stockholm stock exchange, to a large extent due to profits from Losec.