I wouldn't recommend using any fish oil supplement that's expired. Fish oils can become rancid and you may experience gastrointestinal side effects if you ingest them. I believe a large portion of fish oil side effects are caused when people unknowingly use rancid fish oils. These rancid oils are usually found in poorly processed, low-quality fish oil supplements. Using a pharmaceutical-grade fish oil will help you avoid these side effects and exposure to rancid oils; as well as using the products well before the expiry date.