Presence of dark urine without pain may be due to:
1. Diseases of the kidney like glomerulonephritis
2. Medications like aspirin, heparin, certain antibiotics, etc.
3. However, dark urine can also be seen as a side effect of taking Ritalin/ Concerta XL and also on prolonged use of codeine/ paracetamol
or other painkillers.
Consultation with your treating physician will be helpful in this regard.
4. Vigorous exercise can also cause urine to have blood in it due to trauma to the bladder, breakdown of red blood cells, or dehydration
5. Urinary bleeding or dark urine without pain may also indicate some serious disorder like cancer of the Urinary bladder
Investigations like Urine examination & Ultrasound
scan of Abdomen & Pelvis will be helpful in clinching the diagnosis.
Wishing you a Good Health. Let me know if I need to clarify further.
Thanks & take care.