I am having trouble finding the R 126 But I did however find this pill that has a R on one side and 026 on it. Here is the link to a picture of this pill. Check it out if it is the pill you have then what you have is:
Phenobarbital tablets or capsules 15 mg
What are phenobarbital tablets or capsules?
PHENOBARBITAL (Solfoton(R)) is a barbiturate that acts by slowing down the activity of the brain and nervous system. Phenobarbital has sedative and hypnotic properties, which will help make you relaxed and sleepy before surgery or help you to sleep. It also reduces or controls seizures or convulsions, except for absence (petit mal) seizures. Federal law prohibits the transfer of phenobarbital to any person other than the patient for whom it was prescribed. Do not share this medicine with any one else. Generic phenobarbital tablets are available, but not capsules.
If that is not it here is a link to all the white round pills with the R imprint look through the pictures and maybe you can locate your pill.
Sorry I couldnt be of more help
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