This yellow, oval pill imprinted with 131 is a ondansetron 8 MG (ondansetron hydrochloride dihydrate 10 MG) Oral Tablet, per the NIH.
ONDANSETRON HYDROCHLORIDE is a human prescription drug. The active pharmaceutical ingredient is ondansetron hydrochloride and is classified as, "Serotonin 3 Receptor Antagonists [MoA], Serotonin-3 Receptor Antagonist [EPC]."
This pill is made by a total of 6 firms: (1) Sun Pharmaceutical Industries Limited, (2) Unit Dose Services, (3) Rebel Distributors Corp, (4) Lake Erie Medical & Surgical Supply DBA Quality Care Products LLC, (5) Physicians Total Care, Inc., and (6) Bryant Ranch Prepack.
There are 2 other yellow pills that with a similar imprint: "131". They may be a different dosage of the same drug or a different drug entirely.