Is HMB Useful for Building Muscle?

By Aidan MuirOn 18/11/202107/03/2025

Hydroxymethylbutyrate (HMB) is a chemical that is produced when the amino acid leucine is broken down by the body.

It has a few different names depending on the specific version of the molecule. Other names include beta-hydroxy beta-methylbutyric acid, beta-hydroxy and beta-methylbutyrate.

The human body naturally produces it, but typically only produces around 0.3g per day on average. When people supplement it, standard dosages are usually 3-6g per day.

Interest in HMB supplementation started in the early 2000s when a few studies showed significant gains in muscle and strength in comparison to placebo.

There have even been two later studies that have shown gains that are better than what even moderate dosages of steroids provide. So obviously this has generated some interest.

Other research has not been quite as positive. Since the research looks so mixed, this post is intended to summarise whether HMB can be helpful or not.

How Can HMB Theoretically Help?

Supplementing with HMB has been shown to reduce muscle damage and muscle protein breakdown, which obviously can align with the goal of hypertrophy and strength gain.

This mechanism is even stronger for certain phases of training where volume and intensity is significantly higher than normal, and more muscle damage is occurring.

Arguably, this is part of why the research in relation to untrained lifters has typically been significantly more positive than the research on well-trained lifters.

At minimum, long-term HMB supplementation has been shown to be safe. So either it helps a bit, or at least there are no downsides beyond the cost and mild inconvenience of taking it.

Research On Untrained Lifters and Older Populations

Most of the studies on HMB showing significant gains in muscle have been performed on untrained lifters.

Some examples of this are the following studies:

This makes sense since untrained lifters typically accrue more muscle damage than trained lifters. Decreasing the damage and muscle protein breakdown could increase the amount of muscle growth that can occur.

For older populations, the proposed mechanism is that as we age, it becomes easier to lose muscle.

Since HMB is mainly beneficial for reducing the muscle breakdown side of the muscle growth equation, it is more likely to be beneficial under circumstances where people are more prone to muscle loss.

Results in older populations remain inconsistent. A review of seven studies involving 287 older adults found that HMB led to slightly greater muscle growth compared to a placebo. Specifically, the average lean mass gain was only 0.35 kg more over 8–12 weeks.

Making it look even less effective, a review of 10 studies, covering 384 adults over the age of 50 also found little to no effect.

Research on Trained Lifters

A systematic review from 2014 covering all of the studies on trained athletes identified that some studies showed no benefit of HMB on strength and muscle growth and others showed a “trivial” benefit.

The mechanism also makes far less sense for trained lifters than it does for newer lifters. Trained lifters typically experience less muscle damage than newer lifters. Although if you switch training routines or quickly increase volume, this point might become relevant again.

Normally I am in the camp of “if something might work a bit and you are okay with the costs and adding the supplement into your routine, maybe it makes sense for you to take it.” So, the trivial aspect could be worth it for some.

But with HMB there are a few other things to factor in:

It is quite an expensive supplement in comparison to a lot of other supplements.
The consensus from most evidence-based practitioners is to downplay the effectiveness of it, based on looking at the totality of evidence and the mechanisms.
There really is not even a lot of anecdotal support for it. Not many people actually take it, in comparison to the amount of people who swear by other supplements. When things work, usually people start implementing whatever it is that works, before the research actually supports it.
There is controversy amongst some of the studies which should raise scepticism.

A great example of the second point can be seen in the below video from Omar Isuf and Mike Israetel:

The current consensus is that if protein and leucine intake are high enough, HMB is unlikely to further help trained lifters.

Controversy in Studies On HMB

The biggest reason why there has been hype behind HMB is that there are two studies that show extremely positive results. They are massive outliers, and to be honest, seem too good to be true.

As mentioned, the mechanism seems logical for newer lifters but less so for well-trained athletes. This was largely reflected in the research up until around 2014.

Then out of nowhere, one study showed that a group taking HMB was able to gain 7.4kg of lean mass over 12 weeks while dropping their body fat percentage by 6.6%.

Muscle gain and fat loss like that is unheard of without high dosages of steroids.

This same group then published a second study showing even more insane results with 8.5kg of lean mass gained while dropping 8.8% body fat while using HMB and an ATP supplement.

These studies were both done in well-trained lifters.

For context, the below image from Joseph Agu of Elite Nutrition Coaching sums this up well. It compares a study on lifters using 600mg testosterone (a moderate dose steroid cycle) for 10 weeks to studies from this group on ATP alone, HMB alone and HMB + ATP.

Is it not absurd that a supplement that has been around for a long time and is not overly popular, could be more effective than moderately dosed steroids?

To drive another nail into the coffin, the placebo group in the testosterone study made better progress than the placebo group in the HMB study. This indicates that the HMB supplement itself was the key factor influencing the difference. The image below from Stronger by Science illustrates this well.

This result is such an outlier that unless consistently replicated by other research groups, it’s reasonable to largely disregard it. When the majority of studies point in one direction and a single study contradicts them, it’s more logical to trust the broader consensus.

Research On Other Areas

HMB might have benefits for other areas such as sarcopenia related to medical conditions.

In conditions where muscle loss is common, taking HMB appears to be more effective than placebo at preventing this muscle loss. This can be part of why some nutritional supplements used in hospitals such as Ensure contain HMB.

There is also limited evidence that HMB may improve aerobic and anaerobic performance. However, this research is still in its early stages and remains an underexplored area. Additionally, HMB appears to be relatively uncommon among endurance athletes.

How to Take HMB?

If choosing to take HMB, the best way to do it is typically to take ~3g of HMB, 30-120 minutes before training sessions for acute effects in terms of minimising muscle damage.

For the chronic effects, splitting this dosage over 3 servings per day appears to be the best strategy.

As with most supplements, the appropriate dosage depends on body size and muscle mass. Larger individuals will likely need more than 3g, while smaller individuals may require less.

Technically 38mg of HMB per kg of body weight is the consensus dosage, which comes out around 3g for an 80kg individual.

Thoughts on Whether HMB is Beneficial

If those two outlier studies are excluded, HMB appears to be mildly to moderately beneficial for untrained lifters who have started training regularly. It may also help individuals at risk of muscle loss due to bed rest or medical conditions.

The main reason it has not gained traction in the evidence-based community or amongst lifters, in general, is because it does not seem to have much if any, benefit for trained lifters.

If you still wanted to take it though, there is no noticeable downside beyond cost and the actual process of taking it.