Filitra 20 (which contains Vardenafil) is a medication used to treat erectile dysfunction (ED). The most obvious sign that Filitra 20mg is not working is if you are still unable to achieve or maintain an erection sufficient for sexual activity, despite taking the medication. If you take the medication but do not notice an improvement in erectile function within the expected time frame (usually 30 minutes to 1 hour), it may not be working effectively. If Filitra 20 works for some instances but not consistently, there might be issues with absorption, dosage, or other factors that affect its effectiveness.