depot injection

A depot injection is a shot that leaves behind a small reservoir of drug, usually in a muscle or under the skin, which then trickles into the bloodstream slowly over weeks or months. Instead of a daily pill, the patient gets one injection that keeps working for a long time.

The slow release is built in several ways. The drug may be a poorly soluble salt or ester suspended in oil or water, so it must dissolve gradually before it can be absorbed. Or the drug may be trapped in biodegradable polymer microspheres or in a gel that solidifies after injection, releasing the drug as the carrier breaks down. Depot antipsychotics and certain hormonal contraceptives and treatments are well-established examples.

The main benefit is greatly improved adherence, which matters especially for conditions where missed doses are dangerous, and steadier drug levels than daily dosing. The trade-offs are real: once injected the depot cannot be retrieved, so side effects persist until it clears, dose adjustment is slow, the injection itself can be uncomfortable or cause a local reaction, and blood levels may take time to build up at the start of treatment.