What pill is white and round with the letter D on one side and 31 imprinted on the other?

Not Medical Advice:

A round white pill with the imprint D on the front, and 31 on the back of it is 350mg of Carisoprodol (made by Aurobindo Pharma).

Carisoprodol is a Skeletal muscle relaxant that is used to treat muscle spasm, and nocturnal leg cramps.

Abuse of this drug may lead to psychological or physical dependence.

This prescription-only medication may pose a risk to an unborn fetus, and should be used only under a doctor's supervision.

AskDrSears.com offers 5 Tips to Relieve Leg and Foot Cramps without prescription drugs.

Roanoke.com reports that quinine, once used to relieve leg cramps, has been banned for that use by the FDA, leaving it's only use for malaria; some people are very sensitive to quinine toxicity and may develop a rash, blurred vision, dizziness, nausea, headache, or tinnitus after they take it.