Question: Why is it that when you take painkillers you don't well immediately you take them?

David Kirongo answered on 3 Jun 2019:

When a drug is taken orally, it typically takes from 20 minutes to over an hour for it to produce its effect, depending on the drug in question. Other methods like injection can take as little as seconds to minutes to take effect.
A drug’s pharmacological effects can only occur once it has been fully solubilized and has entered the blood stream. For most drugs given orally, the drug must be ingested, pass through the stomach, and into the small intestine, where the drug molecules enter the blood stream through the villi and microvilli. Gastric emptying time can vary from 0 to 3 hours and therefore plays a major role in onset of action for orally administered drugs. For intravenous (injections) drugs, the pathway is much shorter because the drug is administered (usually already in solution) directly to the bloodstream.