Over-the-counter non-steroidal anti-inflammatory drugs such as aspirin, ibuprofen, and naproxen may reduce the effectiveness of selective serotonin reuptake inhibitor (SSRI) antidepressants, a new study has found. SSRIs include such medications as Lexapro, Prozac, and Zoloft and are the most common class of antidepressants prescribed to treat depression. The researchers say the potential interaction between these two types of drugs may help explain why some people do not respond well to SSRIs.