What Are M366 Pills? Name, Dosages, and Effects


If you found a mysterious pill labeled M366 or were prescribed M366 pills and are looking to know more about them, you’ve come to the right place. 

To start, let’s double check you’re looking at an M366 pill. It should be oblong and white with the pill identifier “M366” stamped on one side, and it should be blank on the other side. If your pill matches the description, then you do have an M366 pill. 

Warning: M366 is a prescription medication, meaning you should not take it without a prescription from your doctor. However, some people do take it for fun. While taking a pill now and then won’t kill you, it can be dangerous to take the pills for long periods of time or at high doses for several reasons that I’ll dive into below. I’ll also let you know what it’s used for, the drug name, dosages, brand name, manufacturer, and common side effects.

Before we get into details take a look at the image below to confirm that you have an M366 pill:

Source: NIH


What M366 Pills Are Used For

M366 pills are meant to be used to relieve moderate to severe pain. They’re typically prescribed by your doctor to give you relief from short-term pain. For example, if you just had back surgery, then your doctor might prescribe you M366 pills to help you with the pain from surgery. However, they’re not usually given to patients with long-term pain (such as on-going back pain) because they can be addictive. 

As I said before, some people do use M366 pills recreationally. Some simply start taking the pills for fun; others may have initially received a prescription for the medication and then continue to take it after their prescription has expired because they’ve become addicted. While it won’t hurt you to take one pill, long-term use can lead to addiction, and overdosing can lead to death. I’ll explain more in the section on overuse below.


M366 Drug Name and Dosages

Each M366 pill is composed of 325 mg of acetaminophen and 7.5 mg of hydrocodone bitartrate. 

Acetaminophen is a mild pain reliever and fever reducer. You can buy acetaminophen by itself over the counter (without a prescription); the most commonly known form is Tylenol. It’s not addictive; however, it can cause some negative side effects that I’ll explain below.

Hydrocodone bitartrate is a powerful opioid pain relief medication. It is classified as a narcotic and is highly addictive. It works differently than acetaminophen in relieving pain: “hydrocodone relieves pain by changing the way the brain and nervous system respond to pain.” It binds to specific neurotransmitters in the brain to numb feelings of pain, and, when taken at a high enough dose, it can cause a euphoric high.


Opioid meds block pain in your brain. 


If you’re prescribed this acetaminophen/hydrocodone bitartrate medication by your doctors, they’ll determine your appropriate dose based on your height, weight, and severity of pain. According to the American Society of Health-System Pharmacists, the medication is usually taken every 4 to 6 hours as needed, and if you’re taking the pills on a regular schedule, you should try to take them at around the same times every day. However, follow your doctor’s and/or pharmacist’s instruction. They will know what exact dosing is right for you.

Note: Doctors typically don’t provide prescription refills for acetaminophen/hydrocodone bitartrate due to its addictive nature. If your pain remains severe after finishing your prescribed M366 pills, then talk to your doctor about getting a refill or exploring other pain management options.


M366 Brand Name and Manufacturers

M366 pills are a generic form of acetaminophen/hydrocodone bitartrate. This drug is most commonly known by the brand names Vicodin, Lortab, or NorcoIf you had the brand-name version of the drug, your pill would be stamped with the brand name instead of M366. The generic pills are manufactured by Mallinckrodt Pharmaceuticals.


Common Side Effects

According to the American Society of Health-System Pharmacists, there are mild side effects that some people experience when taking M366 pills. Make sure to tell your doctor if the symptoms continue or get worse:

  • Nausea
  • Vomiting
  • Constipation
  • Drowsiness
  • Dizziness
  • Lightheadedness
  • Fuzzy thinking
  • Anxiety
  • Abnormally happy or sad mood
  • Dry throat
  • Difficulty urinating
  • Rash
  • Itching
  • Narrowing of the pupils

There are some more worrisome side effects that require immediate medical attention:

  • Chest tightness
  • Slowed or irregular breathing

Contact your doctor immediately if you experience one of these symptoms, since they can indicate a severe allergic reaction.


Drugs Interactions to Avoid

There are many drugs (over 700) that can interact poorly with M366 pills. Tell your doctor about all of your current medications (including over-the-counter pills and supplements) to make sure there will be no adverse interaction.

Some of the more common substances known to interact with M366 pills are:

You should also avoid taking additional acetaminophen (such as Tylenol) with this medication because high doses of acetaminophen can lead to liver failure, particularly when combined with alcohol.


Alcohol and M366 pills don’t mix. 


Dangers of Overuse

As I’ve mentioned before, this medication is highly addictive. It’s very important not to overuse this medication. Overuse of acetaminophen/hydrocodone bitartrate can be habit-forming. Weaning yourself off the pills will be extremely difficult as you’ll experience withdrawals. If you’re addicted, talk to your doctor about getting help.

It’s also possible to overdose on the medication. According to the American Society of Health-System Pharmacists, overdose symptoms include:

  • Narrowed or widened pupils
  • Slow, shallow, or stopped breathing
  • Slowed or stopped heartbeat
  • Cold, clammy, or blue skin
  • Excessive sleepiness
  • Loss of consciousness
  • Seizures
  • Death

If you or someone you know is experiencing these symptoms, call poison control at 1-800-222-1222. If the person is unconscious and/or not breathing, call 911.


The Bottom Line on M366 Pills

  • M366 pills are used to relieve moderate to severe short-term pain (i.e. post-surgery).
  • However, some people do use it recreationally. It won’t hurt you to take one pill, but be careful because long-term use often leads to addiction.
  • M366 is a combination of acetaminophen and hydrocodone bitartrate.
  • Acetaminophen is an anti-inflammatory that helps reduce pain and fever; hydrocodone bitartrate is an opioid pain reliever for severe pain.
  • A doctor will determine the appropriate dose for you based on your height, weight, and pain severity.
  • M366 pills are the generic form of the drug; some of the brand name versions are Vicodin, Lortab, and Norco.
  • Many people who take the medication experience mild side effects. However, if you experience chest tightness or irregular or slowed breathing, contact your doctor immediately.  
  • There are over 700 medications that can interact badly with acetaminophen/hydrocodone bitartrate. Talk to your doctor about all of your current medications (including over-the-counter pills and supplements) to make sure there will be no issues.
  • This medication is highly addictive. Talk to your doctor about treatment options if you’re addicted.
  • It’s possible to overdose on this medication, and overdoses can be fatal. Seek immediate medical help if you think you’re overdosing.