The time it takes for Tylenol (acetaminophen) to start working depends on the formulation. Oral preparations must first dissolve in the stomach and then get absorbed into the bloodstream before they have an effect. The approximate length of time it may take before you notice a reduction in your pain if Tylenol is taken on an empty stomach are:

• Orally disintegrating tablets, oral Tylenol liquid: 20 minutes
• Oral tablets, extended-release tablets: 30 to 45 minutes
• Intravenous acetaminophen: 5 to 10 minutes.

If Tylenol is taken on a full stomach it may take up to twice as long for it to have an effect, depending on the preparation. Generally, it takes longer for Tylenol to reduce fever than it does for it to relieve pain.