As with any medication, some people might experience side effects. The most common ones while taking sildenafil are headaches, flushing, upset stomach, blurred vision, nasal congestion, nausea, muscle and back pain. In case you experience any of these side effects, they shouldn’t last a long time, your body is just adjusting to the drug. Of course, if any of these persist, you need to consult your doctor or pharmacist at Hims.