A system to determine medication adherence may include a chemical marker sensor, a verification sensor, and a processor. The chemical marker sensor may be configured to detect one or more markers in sweat vapor of a user. The verification sensor may be configured to detect whether the system is in use. The processor may be communicatively coupled to the chemical marker sensor and the verification sensor and may be configured to determine whether the user has taken a therapeutic agent that includes the one or more markers based on signals generated by the chemical marker sensor and the verification sensor.
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