| OAS | old age security; oral allergy syndrome; osmotically active substance |
|---|---|
| OLS | oubain-like substance |
| PGS | peristent gross splenomegaly; Pettigrew syndrome; plant growth substance; postsurgical gastroparesis... |
| PLS | Papillon-Lefevre syndrome; polydactyly-luxation syndrome; preleukemic syndrome; primary lateral scle... |
| PSDA | Patient Self-Determination Act; psychoactive substance abuse and dependence |