How does morphine work?

Morphine works by affecting the receptors of the nervous system and results in sedation and pain relief. More on how morphine works in the body and nervous system here.

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Morphine is used in medicine for sedating patients with acute, or chronic conditions. The milky substance found in the seedpod of the poppy plant is the natural source of morphine. When dried, it is used for making opium, which contains morphine, together with other alkaloids. But how does morphine work, exactly? We review here and invite your questions about morphine at the end.

How does morphine work in the body?

In general, the use of morphine results in relief from physical pain. But morphine can also arouse the cough reflex and give the feeling of constant hunger. After administration is absorbed into the blood and morphine stays in the body and is delivered to all its organs.  Many people don’t know that there is lower concentration of morphine in the brain and muscles compared to the kidneys, lung and liver. And a small portion goes directly to the milk of nursing women.

How does morphine affect the brain and nervous system?

The biggest effects of taking morphine take place in the receptors of the nervous system. Different branches of receptors (m, k and d) are involved in various actions, urges, and processes on a molecular level.

m 1-receptors are involved in:

  • analgesia
  • euphoria
  • decreased gastrointestinal activity
  • miosis
  • pain modulation
  • respiratory depression

m 2-receptors are involved in:

  • drowsiness
  • mental clouding
  • nausea
  • respiratory depression

k-receptors are involved in:

  • analgesia
  • diuresis
  • dysphoria
  • mild respiratory depression
  • miosis
  • sedation

d-receptors are involved in:

  • analgesia
  • delusions
  • dysphoria
  • hallucinations

How fast or quickly does morphine work?

There are many ways to take morphine, such as oral, intravenous or rectal. And the speed at which morphine works depends on the dose and the route of administration. For example, morphine injection has nearly instantaneous effect. But in, general, it could take from 15 to 60 minutes for the effects of morphine to manifest.

How long does morphine work?

Morphine actually has a short half life of 1.5 to 7 hours, except for patients who are renally impaired. (who can feel the drug effects longer than usual). Effects of narcosis and analgesia (loss of sense of pain and not loosing consciousness) can last longer for older patients.

One of the measurable effects of morphine use is gastric activities, especially constipation. In this way, morphine works to hold on to food forlonger than 12 hours, while the absorption of other orally administered drugs is totally disabled. Additionally, the normal sensitivity of the respiratory system is stabilized within 2 to 3 hours after morphine use, but the capacity of the air volume remains unstable for up to 5 hours.

How does morphine work better?

Morphine is available in several prescribed forms, such as injections, oral solutions, tablets and capsules etc. Since it is considered to be a strong painkiller, often users take bigger doses of morphine than prescribed. While there is no strict upper limit to morphine that is safe, an oral dose of 0.3g to 0.4g or morphine can be lethal.

Does morphine work for everyone?

Yes, morphine can work for everyone as a sedative and pain reliever. However, it works for everyone differently, depending on a few factors. One factor is dosage, which will be different for each individual. For example, someone who is opioid tolerant, can take higher doses of morphine than an opioid naive person.Other factors are the route of administration, previous exposure to morphine and development of signs of addiction to morphine. Once a patient is tolerant to one opiate, s/he develops tolerance to other opiates and opioids.

Morphine use questions

Do you still have questions about using morphine or how morphine works? Please leave your questions or comments in the section below. We do our best to respond to you personally and promptly.

Reference Sources: Medline Plus: Oral Morphine
PUBCHEM: Morphine
Prosecuting Attorney Institute: Morphine drug data sheet
About the author
Lee Weber is a published author, medical writer, and woman in long-term recovery from addiction. Her latest book, The Definitive Guide to Addiction Interventions is set to reach university bookstores in early 2019.


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  1. Hi, I have been on prescription morphine to control lower back pain. I also feel that my mental facilities have become foggy. Also, my memory seems to be affected. Is there some way to continue my pain meds and clear up the foggy , and memory issues. I read everything I can get my I Pad to download. I play word games with my wife. All to try and rejuvenate my cerebral issues. Is there some other method to control pain other than mind fogging morphine? Help, I cannot fix myself. Thx. Tom C.

  2. I have recently had an operation on my foot which I understand was quite involved. After the operation about forty mins I started vomiting it was horrendous bringing up nothing but air, I felt unbelievably ill, so I’ll in fact I refused any further medication but I did have water to sip after a very small sip of water I started vomiting again. Two and half hours or so a drip was put up(Hartman’s) I continued vomiting till four in the morning, by which time I had stopped sipping water and gave permission for an antiemetic to be given IV. My question is,Was it the amount of Morphine I was given which had slowed my intestine activity to near nil that caused such a horrendous long vomiting episode?

  3. My husband had a stroke in Dec 2012. It affected his left side. In March of 2013 he started to have very bad pain on his left side, from shoulder down to his foot. He can’t sit and can only stand for a few minutes. He takes 1ml. of liquid morphine every 4 hours but this does relieve the pain. He’s been told it could be nerve pain. Doesn’t morphine help with nerve pain?

  4. I am allergic to any meds that contain acetaminophen. I can’t tolerate tramadol. I pulled muscles in left thigh, buttocks, etc. I took 5mg.oxycodone w/food & had the dry heaves. It really did not help w/pain. Will morphine work o n me?

    1. Hi Mary. It should work well as it blocks even more severe pains. But, I still think you should first ask your doctor about any other acetaminophen-free pain killer solutions.

  5. I was prescribed morphine for severe arthritis. However, it did not relieve any of my pain. But I had many of the side effects of morphine, such as brain fog, intermittent memory loss, poor judgment, sharp abdominal pain and constipation. I had no sedative effect and actually had sleep problems where I was unable to sleep at all for about three days in a row. Then I would sleep perhaps a few hours. Then unable again to get needed sleep. Therefore, I did not stay on morphine for a long period of time. Exalgo and hydromorphone actually worked to relieve my pain to a great degree, but not 100%, but peperhaps 60% or about that. But I did have some concerned side effects, so for me narcotics are not for me. I quit taking opiates totally and only take tramadol in addition to cortisone back infections which provides adequate pain relief and seemingly without any side effects.

    1. Hi Joanne. Morphine doesn’t always work 100% for everybody. I’m glad your current treatment is working for you.

  6. Hello Viki. I’ve read that opiate dependence can develop after chronic, constant, daily dosing within a week, or two. While each person is unique, regular dosing will take users from opioid naive to opioid tolerant within a few weeks of round the clock dosing.

  7. Hello,

    Could you tell me how long someone would need to be on Morphine to become somebody who is opioid tolerant rather then opioid naive ?


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