Hi, I don t think darkening of your knuckles is related to the medication you are taking even though some drugs may make the skin darker over knuckles. The drugs you are taking are not known to cause it however you can give a try of changing the drugs for pain and see if it helps. There is another condition where knuckles are darker called acanthosis nigrans. The skin appears darker and velvety. It is a prediabetic condition and usually armpits & neck are more affected than knuckles. I would advise you to get your sugar levels tested to rule it out. In some people knuckles are darker than usual and it could be due to the friction of the area while using your hands. In some cases there is vitamin B12 deficiency and in many cases there is no reason for it. Please get your B12 levels checked and if the levels are low then you can take vitamin B12 tabs or injections. If there is no abnormality in any of the above, then you may ignore it. I would advise you to apply some moisturizer after using a scrub over the area to keep the area soft and moisturized. It may reduce the pigmentation. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Anoop Kumar, General & Family Physician