This 1998 coin commemorates the 100th anniversary of the Ministry of Health.
The head-on elephant on the reverse is a classic image of Indra -- a guardian deity of Buddhism -- riding Airavata, his mythological white elephant. In this case, Airavata is depicted with a single head and trunk, but four tusks. It is also known as Erawan in Thai, but in that guise has three heads.
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