Drug Interactions It is important to know the potential drug interactions that may occur when taking C20 Pill. Following these precautions and warnings, you can safely take C20 Pill as your doctor prescribes and enjoy its benefits for erectile dysfunction. It should not be taken by men taking nitrates or alpha-blockers. Back pain or muscle aches Nasal congestion or runny nose Vision changes, including blurred vision or difficulty distinguishing blue and green colours Hearing loss or ringing in the ears While these side effects are relatively common, they usually go away within a few hours. Do not take C20 Pill if you are allergic to tadalafil, the active ingredient in Cialis. Warnings: C20 Pill should not be taken by men who have an allergy to Tadalafil or any other ingredients in the medication.Enter the imprint code that appears on the pill. Example: L; Select the the pill color (optional). Select the shape (optional). Alternatively, search by drug name or NDC code using the fields above. Tip: Search for the imprint first, then refine by color and/or shape if you have too many results. Cialis Pill Images. Note: Multiple pictures are displayed for those medicines available in different strengths, marketed under different brand names and for medicines manufactured by different pharmaceutical companies. Multi-ingredient medications may also be listed when applicable. C Pill – yellow round, 6mm. Pill with imprint C is Yellow, Round and has been identified as Mirtazapine mg. It is supplied by Caraco Pharmaceutical Laboratories. Mirtazapine is used in the treatment of Depression; Major Depressive Disorder and belongs to the drug class tetracyclic antidepressants. Risk cannot be ruled out during pregnancy.