How long does morphine last?

Morphine’s duration of action varies between 1.5 and 4.5 hours but can be longer when used in higher doses or for longer periods of time. More on morphine effects here.

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Therapeutic effects of morphine generally last for about 4 hours, although duration of action is related to mode of administration as well as details about individual dosing.

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Then, we invite your questions about morphine, including signs of morphine addiction and getting treatment for morphine addiction, at the end.

Morphine effects on the body and brain

Morphine induces a wide range of pharmacologic effects on the body and brain such as analgesia, euphoria, somnolence, respiratory depression, diminished gastrointestinal motility and physical dependence. However, morphine also has the potential to change the way the brain functions. Why is this?

This is because morphine acts on the central nervous system in different ways, affecting the m-receptors, the k- and d-receptors respectively. Additionally, analgesia induced by morphine is activating at least three areas of the central nervous system: the periaqueductal-periventricular gray matter, the ventromedial medulla and the spinal cord.

Morphine, when administered according to a schedule, may affect from one to all three areas at once, which will manifest a greater number of effects. In terms of specific effect on the body, the m-receptors are responsible for the modulation of pain, analgesic effects, respiratory depression, miosis, feeling of euphoria, and decreased gastrointestinal activity. The group of m 2-receptors is involved in drowsiness, nausea, and mental clouding while the k-receptors are involved in analgesia, diuresis, sedation, dysphoria. The d-receptors are also affected by morphine and are involved in delusions and hallucinations.

Morphine duration of action

The terminal half-life for morphine varies between 1.5 and 4.5 hours. However, patients have reported much longer duration of action due to higher dose administration or protracted use. Keep in mind that (for all modes of administration) late respiratory depression can occur up to 24 hours after administration of morphine.

Epidurally injected as part of anesthesia, morphine acts really strong and fast, due to the circulation of morphine in spinal fluids, which get directly to the brain. In such cases peak plasma concentrations are reached within 15 minutes after administration of 3mg of morphine.

How long do morphine effects last?

Duration of action of the effects of morphine depend upon the mode of administration. When morphine is administered through epidural injection into the spinal fluid, it has a terminal half-life varying from 39 to 249 minutes. That is a bit shorter range compared to intravenous or intramuscular injection of 1.5 to 4.5 hours. And believe it, or not, only 4% of the morphine dose reaches to the brain. After intrathecal bolus injection of morphine, there is a rapid distribution phase of 15 to 30 minutes and a half-life in the of 42-136 min.

How long does a morphine high last?

Euphoric effects of morphine last for 4 to 6 hours. Onset of morphine effects takes place in 15 to 60 minutes. One interesting fact about morphine use is that as you grow older, the analgesia will last longer even with the same dose of morphine administered and you will experience the same high effects.

Morphine time in the body

A regular morphine user begins to eliminate morphine within 2 hours of administration of a single dose. Only 36% of morphine binds with proteins and 54% for muscle tissue. Excreted by the kidneys through urine in about 90%, only 10% are left to feces to eliminate morphine out of the body. However, up to 12% of morphine manages to leave the body without being metabolized and remains unchanged and can be recovered in the urine. In terms of drug testing, morphine can be detected in urine based drug tests up to a day or two after dosing.

Morphine high effects

As with any other drug, euphoric effects depend on the dose of morphine is administered, the route is taken, the history of drug abuse and dependence, the level of tolerance developed to morphine etc. Here is a list of the most common effects that can occur even as you feel effects of euphoria.

  • analgesia
  • constipation
  • cramping
  • depressed consciousness
  • depressed heart rate
  • diminished reflexes
  • drowsiness
  • euphoria
  • flushing of face and neck
  • lethargy
  • mental clouding
  • nausea and vomiting
  • pupils fixed and constricted
  • reduced gastrointestinal activity
  • relaxation
  • respiratory depression
  • sedation
  • sweating

Morphine duration questions

Do you still have questions about the duration of action of morphine, its excretion, or effects? We invite you to use the following section for your comments and questions. We try to respond with a personal and prompt answer ASAP.

Reference Sources: Hazardous Susbstances Data Bank TOXNET: Morphine
National Highway and traffic Safety Administration: Morphine (And Heroin)
Daily Med: Astramorph (morphine sulfate) Injection [AstraZeneca LP]
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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