Mersyndol: Ingredients, Uses, Dose, Side Effects, Addiction

Mersyndol is a combination pain medication for short-term use to relieve moderate pain and fever. Mersyndol’s analgesic effect relieves pain and tension. It is used for the relief of moderate to severe pain including toothache or pain from injury or surgery, and for the temporary relief of headache. In addition, the calmative properties of Mersyndol may be especially useful in the treatment of tension headache, migraine, and period pain.

How Mersyndol works

Each tablet of Mersyndol contains the active ingredients paracetamol, codeine phosphate hemihydrate, and doxylamine succinate. Paracetamol is a simple painkilling medicine used to relieve mild to moderate pain. Despite its widespread use for over 100 years, we still don’t fully understand how paracetamol works to relieve pain. However, it is now thought that it works by reducing the production of prostaglandins in the brain and spinal cord.

The body produces prostaglandins in response to injury and certain diseases. One of the effects of prostaglandins is to sensitize nerve endings, causing pain (presumably to prevent us from causing further harm to the area). As paracetamol reduces the production of these nerve-sensitizing prostaglandins, it is thought it may increase our pain threshold, so that although the cause of the pain remains, we don’t feel it as much.

Codeine phosphate is a slightly stronger painkiller known as an opioid. Opioid painkillers work by mimicking the action of naturally occurring pain-reducing chemicals called endorphins. Endorphins are found in the brain and spinal cord and reduce pain by combining with opioid receptors. Codeine mimics the action of natural endorphins by combining with the opioid receptors in the brain and spinal cord. This blocks the transmission of pain signals sent by the nerves to the brain. Therefore, even though the cause of the pain may remain, less pain is actually felt.

Doxylamine is a type of medicine called a sedating antihistamine. It is included in Mersyndol not so much for its antihistamine effect, as for its sedative effect. Doxylamine is known as a sedating antihistamine because it enters the brain, where it causes drowsiness. This feature can be useful if the pain is preventing restful sleep.

Mersyndol Tablet improves the patient’s condition by performing the following functions:

•          Increasing the pain threshold and increases the blood flow across the skin, heat loss, and sweating.

•          Antagonizing the adenosine receptors.

•          Breaking down codeine by the liver into morphine.

•          Blocking the effects of the chemical histamine and a few others in the body.


How is Mersyndol taken?

The standard dose of Mersyndol for adults and children 12 years or over is one or two tablets/caplets every 4-6 hours as needed for pain relief.

This medicine contains codeine which can cause addiction if you take it continuously for more than 3 days. If you take this medication for headaches for more than 3 days, it can make them worse.

What happens if I miss a dose?

Since this medicine is used when needed, you may not be on a dosing schedule. Skip any missed dose if it’s almost time for your next dose. Do not use two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. A codeine overdose can be fatal, especially in a child or other person using the medicine without a prescription. Overdose symptoms may include slow breathing and heart rate, severe drowsiness, muscle weakness, cold and clammy skin, pinpoint pupils, and fainting.

Can a pregnant or breastfeeding woman take Mersyndol?

No, Mersyndol is not recommended for use during pregnancy. Do not take Mersyndol while you are breastfeeding. Codeine and morphine pass into breast milk.

What are the possible side effects of Mersyndol?

Stop taking Mersyndol and see a doctor straight away if you get any of the following side effects:

• You get swelling of the hands, feet, ankles, lips, or throat which may cause difficulty in swallowing or breathing. You could also notice an itchy, lumpy rash (hives) or nettle rash (urticaria). You may be having an allergic reaction to the medicine.

Tell your doctor straight away if you notice any of the following side effects:

• You have rash, fever, swelling, bruising, or tiredness

• You develop yellowing of the skin or the whites of the eyes

• You have severe abdominal pain which may reach your back. This could be a sign of inflammation of the pancreas (acute pancreatitis)

• You get infections or bruises more easily. This could be because of a blood problem.

• You experience blistering or bleeding of the skin around the lips, eyes, mouth, nose, and genitals. Also flu-like symptoms and fever. This may be something called Stevens-Johnson syndrome.

• You have a severe blistering rash where layers of the skin may peel off to leave large areas of raw-exposed skin over the body. Also a feeling of being generally unwell, fever, chills, and aching muscles. This may be something called ‘Toxic epidermal necrolysis’. Very rare cases of serious skin reactions have been reported.

Tell your doctor or pharmacist if any of the following side effects gets serious or lasts longer than a few days:

• Constipation

• Headache

• Drowsiness, fatigue

• Dizziness

• Restlessness

• Twitching or tightening of muscles

• Difficulty or pain passing urine

• Dry mouth

• Blurred or double vision/visual disturbances

• Ringing in ears (tinnitus)

• Feeling or being sick

• Diarrhoea

• Thick phlegm

• Low blood pressure (causing lightheadedness or fainting when standing up)

• Confusion

• Depression/mood swings

• Difficulty sleeping,

• Shaking/fits

• Irregular heartbeat

• Palpitations

• Stomach pain

• Sweating

• Facial flushing

• General discomfort

• Loss of appetite (anorexia)

• Very slow or shallow breathing, shortness of breath

• Hallucinations, nightmares

• Cramps or stiffness

• Codeine dependence

• Not being able to pass water (urinary retention)

Prolonged use can lead to worsening headaches. If you feel you are reacting badly to this medicine in any way, stop taking the tablets and tell your doctor or pharmacist.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

How do I know if I’m addicted?

If you take Mersyndol according to the instructions on the pack, it is unlikely that you will become addicted to the medicine. However, if the following applies to you, it is important that you talk to your doctor:

• You need to take the medicine for longer periods of time.

• You need to take more than the recommended dose.

• When you stop taking the medicine you, still feel very unwell but you feel better.

What medications can interact with Mersyndol tablet?

If you use other drugs or over-the-counter products at the same time, the effects of Mersyndol Tablet may change. This may increase your risk for side effects or cause your drug not to work properly. Tell your doctor about all the drugs, vitamins, and herbal supplements you are using, so that your doctor can help you prevent or manage drug interactions.

Mersyndol Tablet may interact with the following drugs and products:

•          Adderall

•          Alcohol

•          Antianxiety agents

•          Anticholinergics

•          Antiemetics

•          Antihistamines

Mersyndol Tablet – Contraindications

Hypersensitivity to Mersyndol Tablet is a contraindication. In addition, Mersyndol Tablet should not be used if you have the following conditions:

•          Acute or severe bronchial asthma

•          Alcohol consumption

•          Children less than 12 years of age

•          Hepatic impairment

•          Hypercarbia

•          Hypersensitivity


Dr. Oche Otorkpa PG Cert, MPH, PhD

Dr. Oche is a seasoned Public Health specialist who holds a post graduate certificate in Pharmacology and Therapeutics, an MPH, and a PhD both from Texila American University. He is a member of the International Society of Substance Use Professionals and a Fellow of the Royal Society for Public Health in the UK. He authored two books: "The Unseen Terrorist," published by AuthorHouse UK, and "The Night Before I Killed Addiction."
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