What is extended release vs immediate release?

Last updated September 3, 2026.

Immediate release dissolves fast, peaks within about an hour, and may need several doses a day; extended release (ER, XR, SR, LA) meters the drug over many hours for smoother levels and once-daily dosing. ER versions cut peak-linked side effects and simplify schedules; immediate versions act faster and dose flexibly. Extended pills are engineered structures, so the NHS warns never to crush or open them without medical advice: it dumps the whole dose at once. If the pharmacy swaps forms, confirm the switch was intentional. No code on the bottle means immediate release.

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