The time of expiration of Merlin after opening the cap is more difficult to answer. It is recommended to use it within 1-2 months after opening the cap and not recommended to use it beyond 2 months. Merlin itself is placed in solution and can remain relatively long. If the cap is not opened, there is a period of almost three years from the day of production of Merlin until it expires. The main ingredient in Merlin is ibuprofen, which is very stable in solution and has a very long expiration time. However, Merlin, as an ibuprofen suspension, oral solution, is easily contaminated by bacteria after opening the cap, causing deterioration of the drug. So there is no clear time how long Merlin expires after opening the cap, it may take 1-2 years or even 2-3 years to expire. Oral suspensions are recommended to be used within 1-2 months after opening the cap to prevent the drug from being contaminated by bacteria and deteriorating. Merlin is recommended not to be left for too long after opening the cap. The sodium benzoate inside acts as a preservative and its efficacy may be lost, leading to contaminating bacteria in the medicine, which is not good for human health.