What Are the Effects of Morphine?

Morphine is a narcotic pain reliever derived from the opium poppy plant. It is highly effective for short-term pain relief and easing cancer-related pain. The effectiveness of morphine for chronic pain management is controversial as the balance between potential benefits versus risks is often a fine line. In deciding whether morphine is a good therapeutic option, all of its many effects on the body have to be taken into consideration.


Morphine is a powerful pain reliever. Its physical structure is similar to naturally occurring pain relievers in the brain allowing morphine to mimic their actions. The drug effectively reduces pain sensation and alters the psychological and emotional responses to pain. However, when morphine is taken over a prolonged period, increasingly higher doses are required to provide an equivalent level of pain relief. This effect–known as morphine tolerance–limits the effectiveness of the drug for the management of chronic pain.

Nausea and Vomiting

Morphine stimulates an area in the brain called the chemoreceptor trigger zone (CTZ). This center provokes nausea and vomiting. Some people are unable to tolerate morphine because it causes them to have intense nausea and vomiting. Others have a minimal level of nausea, which decreases with repeated administration of the medication.

Slowed Stomach and Intestinal Activity

Morphine slows all normal gastrointestinal activity. Under the influence of morphine, the stomach empties more slowly than usual and movement of digesting food through the small intestine is prolonged. Fecal material transit through the colon slows. Slowed activity of the large intestine frequently causes constipation.

Drowsiness and Decreased Mental Sharpness

All narcotic medicines, including morphine, produce drowsiness. The drug is a central nervous system depressant, meaning it slows brain activities. This effect is apparent to both the person taking the medication and to others around her. Drowsiness and overall mental slowness are the norm when morphine is in the body. People taking morphine for a prolonged period typically develop some tolerance to these effects of the drug.

Immune System Suppression

Short and long-term morphine use suppresses immune system responsiveness. Immune cells have opioid receptors on their surface; morphine and other narcotics interact with these receptors, thereby having direct effects of their function.

Hormonal Changes

Morphine and other narcotics can decrease circulating levels of hormones including estrogen, testosterone and other sex hormones. Reduced levels of adrenal gland hormones such as cortisol also occur. Decreased testosterone levels in men on morphine may cause loss of interest in sexual activity, erectile dysfunction, and low energy levels. Low estrogen levels in women on morphine can cause menstrual irregularities and decreased sex drive.

About this Author

Tina Andrews has been a medical writer and editor since 2000. She has published in “Cancer,” “Ethnicity & Disease,” and “Liver Health Today,” and was formerly a medical officer with the Centers for Disease Control and Prevention. Andrews holds a Doctor of Medicine degree and a Bachelor of Arts in chemistry.