The half-life of morphine is 2 hours. How long does it take for morphine to reach a steady state if the dose remains constant?

To understand how long it takes for morphine to reach a steady state, it's essential to know that steady state is generally achieved after approximately 4 to 5 half-lives of a drug. The half-life of morphine is given as 2 hours, so we can calculate the time to steady state.

If we multiply the half-life by 4, we get:

• 4 half-lives: 4 x 2 hours = 8 hours

Continuing to 5 half-lives yields:

• 5 half-lives: 5 x 2 hours = 10 hours

Since steady state typically occurs closer to the 4 to 5 half-life mark, the correct amount of time for morphine to reach steady state with consistent dosing is 10 hours. This is why the correct answer is precisely 10 hours. It reflects the pharmacokinetic principle that the accumulation of the drug in the bloodstream will lead to balanced drug levels over time, ensuring a consistent therapeutic effect without toxicity.