Do Pain Killers Put the Brakes on Muscle Growth?

Over-the-counter pain killers are a popular way to ease the pain and soreness that manifests itself 24-48 hours after a tough workout.

But there’s a lot of debate about what impact they have on muscle growth.

On the one hand, you have research evidence that pain killers reduce protein synthesis after training. And on the other, studies to show that taking pain killers for several months actually speeds up gains in muscle size and strength.

If you want to build muscle, will pain killers help or hinder your progress?

The way in which pain killers are thought to affect gains in muscle mass is by limiting the rise in protein synthesis that normally occurs after exercise.

In simple terms, your muscles grow larger when protein synthesis is greater than protein breakdown.

Think of your muscles a bit like your bank account. Money coming into your account is known as protein synthesis. Money leaving the account is known as protein breakdown.

When there’s more money coming into your account than there is going out, you’ll end up with a bigger bank account. In much the same way, when protein synthesis exceeds protein breakdown, you’ll end up with bigger muscles.

Although there are a few studies linking pain killers to a reduced rate of protein synthesis, the one I want to look at in more detail comes from a research group led by Professor Todd Trappe.

A group of men with an average age of 25 were assigned to one of three groups. All groups performed 10-14 sets of 10 eccentric leg extensions.

  • After completing the workout, group one received the maximal over-the-counter dose of ibuprofen (1200 milligrams daily).
  • Group two was given acetaminophen (4000 milligrams daily).
  • The third group received a placebo (a “dummy” supplement) that contained no active ingredients.

When muscle samples were analyzed 24 hours after exercise, the increased rate of muscle protein synthesis normally seen after resistance exercise was reduced in subjects given the pain killers.

You can see this for yourself in the figure below, which shows muscle protein synthesis before (white bars) and after (black bars) exercise (ACET = acetaminophen group; IBU =ibuprofen group; PLA = placebo group).

pain killers protein synthesis

In other words, it appears that pain killers can limit the ability of your muscles to synthesize protein and repair themselves after exercise. And if they inhibit recovery, they also have the potential to put the brakes on muscle growth.

However, this was a short-term study that looked at protein synthesis in subjects using pain killers for just 24 hours.

And while this type of research is useful when it comes to generating ideas and theories about what might happen over a longer period of time, it’s only one piece of the puzzle.

A follow-up study, this time lasting three months, shows that a daily dose of pain killers actually ACCELERATES gains in both muscle size and strength.

Researchers tracked 36 men and women between the ages of 60 and 78. Subjects were randomly divided into an acetaminophen group, an ibuprofen group or a placebo group. The two drugs were consumed at recommended daily dosage levels.

To the research team’s surprise, an analysis of muscle tissue samples taken before and after the training program revealed that those taking the pain killers gained more muscle mass than the placebo group.

Should you run out and start downing over-the-counter pain killers in an attempt to boost muscle growth?

I don’t think so, as there are a few issues with this latter study that limit the conclusions we can draw.

Firstly, the researchers measured muscle growth using something called a muscle biopsy, which involves taking a slice of muscle tissue from the body and looking at it under a microscope. However, isolated tissue samples from an individual muscle give you a very limited picture about what’s happening to muscle growth in the whole body.

In addition, the training program involved 15-20 minutes of leg extensions three times a week. That’s not the type of routine most people would use if they were trying to build size and strength.

What’s more, the people taking part in the study were in their sixties and seventies. We can’t assume that the results will apply to younger people in their twenties, thirties and forties.

Finally, elderly people will often suffer from age-related aches and pains. The pain killers may simply have allowed them to train harder during each workout, which could have contributed to the extra gains in muscle size and strength.

The last study I want to look at comes from a group of Canadian researchers who examined the impact of a more moderate dose of ibuprofen (400 milligrams per day) on gains in muscle size and strength.

Twelve men and 6 women (approximately 24 years of age) trained their right and left biceps on alternate days (6 sets of 4-10 repetitions), 5 days a week for 6 weeks. They received a daily dose of 400 milligrams of ibuprofen immediately after training their left or right arm, and a placebo after training the opposite arm the following day.

Did ibuprofen help or hinder muscle growth?

It actually did neither. Biceps muscle thickness in the ibuprofen arm went from 3.63 to 3.92 centimeters. That’s an increase of 8%, which was no different to the placebo arm. Gains in muscle strength were also much the same in the ibuprofen and placebo groups, with both groups posting roughly a 20% average gain in strength.

To quote the researchers directly:

A moderate dose of ibuprofen ingested after repeated resistance training sessions does not impair muscle hypertrophy or strength and does not affect ratings of muscle soreness.

The explanation for ibuprofen’s lack of effect, positive or negative, is most likely due to the dosage used. The earlier research by Professor Trappe used maximum over-the-counter doses (1200 milligrams of ibuprofen per day). This Canadian study used just one-third of that amount (400 milligrams per day).

Quite apart from their impact on muscle growth, there are a couple of other downsides to anti-inflammatory pain killers (NSAIDs).

Firstly, NSAIDs appear to have a negative impact on the health of connective tissue. One study shows that NSAID use (2 x 100 milligrams Indometacin daily for 7 days) abolished the adaptive increase in collagen synthesis in the patella tendon normally seen after exercise.

Used for prolonged periods, NSAIDs could increase your risk of injury further down the line, either by weakening connective tissue or limiting its ability to adapt to exercise.

NSAIDs work by inhibiting the production of prostaglandins, which are involved in pain. However, those same prostaglandins also play a role in the creation of collagen, which is the building block of most tissues.

The effect of NSAIDs on collagen synthesis helps to explain why they’ve been shown to slow the healing of injured muscles, tendons, ligaments and bone.

There’s also some interesting animal research to show that inflammation plays a vital role in healing damaged muscle tissue. The presence of inflammatory cells is linked to higher levels of insulin-like growth factor-1 (IGF-1) which increases the rate of muscle regeneration.

We’ve known for some time that excess anti-inflammatory medication, such as cortisone, slows wound healing. This study goes some way to telling us why: IGF-1 and other materials released by inflammatory cells actually help with the healing process. For wounds to heal we need controlled inflammation – not too much, and not too little.

What’s the bottom line?

The extent to which the prolonged use of pain killers affects muscle growth over a period of several weeks or months is open to debate. However, there is mounting evidence that high doses may extinguish the fire that sparks muscle growth after exercise.

While the occasional use of pain killers in moderate amounts isn’t likely to suppress your gains completely, they’re certainly not something you should use too often. Large doses taken on a regular basis could easily add up to a negative impact on muscle growth in the long run.


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Christian FinnChristian Finn holds a master's degree with distinction in exercise science, is a former personal trainer and has been featured on BBC TV and radio, as well as in Men's Health, Men's Fitness, Fit Pro, Zest, and Perfect Body magazine.