Take back events will be held at fire stations, health centers, police and sheriff's departments, and other law enforcement offices and other city and county agencies in all Bay Area counties between 10 a.m. and 2 p.m.
The day is an opportunity for residents to prevent pill abuse and drug theft, and dispose of the medications in an environmentally friendly way.
Participants can drop off unwanted medications at no cost and anonymously.
Intravenous solutions, injectables and needles will not be accepted.
Last September at the same federal Drug Enforcement Agency-sponsored events, 244 tons of prescription drugs were brought in at more than 5,200 sites nationwide.
Union City police said this is the third year the city has participated in the event. At the fall event last year, 165 pounds of prescription drugs were collected at a drop-off in the city.
On Saturday, drop-offs can be made at the Union City Police Department at 34009 Alvarado Niles Road.
For a full list of drop off locations throughout the Bay Area click here.