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In this Optimum Nutrition Serious Mass review, we had GGR performance editor Anthony O’Reilly, CPT, CNC, test out this popular sports nutrition weight gainer. He rotates this in with other protein powders, especially on heavy, bodybuilding-style training days.

If you are a hard gainer, getting in the extra calories you need to put on weight can be taxing and downright sickening. This is where a weight gainer like ON Serious Mass can come in handy as it can help you boost your calorie intake significantly with one protein shake. 

That said, please remember that most of your caloric needs should be coming from food with sports nutrition supplements like Serious Mass simply filling in the gaps. Protein powder generally contains few nutrients and muscle growth happens best when a diet is nutrient-dense. Basically, just choose a good old peanut butter and jelly sandwich over a mass gainer whenever possible. 

Medical disclaimer: This article is intended for educational and informational purposes only. It is not intended as a substitute for medical advice. For health advice, contact a licensed healthcare provider. GGR also recommends choosing a product that has been third-party tested for quality.

We’re In the Game of Making Gains

With dozens and dozens of protein powders tested and reviewed, we know a thing or two about how to get in your amino acids. Our team of bodybuilding experts, nutrition professionals, and real-life fitness enthusiasts try the products we review and relay both the good and the bad of what we find, so you don’t waste your time or money.

Optimum Nutrition Serious Mass

Optimum Nutrition Serious Mass

GGR Score: 3.975 starstarstarstarstar

Product Highlights

  • High-calorie supplement formulated with a 1:5 protein to carbohydrate ratio
  • Each serving contains 1,250 calories
  • Each serving contains 50 grams of protein, 253 grams of carbohydrates, 4 grams of fat,
  • Available in Chocolate, Chocolate Peanut Butter, Strawberry, and Vanilla 
  • Recommended to use 2 scoops per 24 ounces of fluid taken post-workout or in between meals

Pros & Cons


  • Taste
  • High carb to protein ratio
  • Includes creatine monohydrate
  • Low fat
  • Users report it works quickly


  • Does not mix well without a blender
  • Contains sucralose
  • 20 grams of sugar

Bottom Line

If you do not mind artificial ingredients, Optimum Nutrition Serious Mass is a good-tasting weight gainer with an impressive 1:5 protein to carbohydrate ratio.

A Quick Look at Optimum Nutrition Serious Mass Weight Gainer

Optimum Nutrition, or ON, is one of the most popular sports nutrition brands in the bodybuilding and fitness community due to its general affordability, simple and high-quality formulations, and accessibility. I remember using the strawberry whey as my staple when I first started lifting in college and I swore by it. So, how does their high-calorie protein powder measure up to these standards?

Before You Buy

  • It has a large 2.5-cup serving size, which is standard for most mass gainers, but requires you to own a blender if you want the best experience.
  • Plan out how often you are going to use it ahead of time, as re-ordering often can get very expensive.
  • It uses whey concentrate, which may cause tummy issues for those sensitive to lactose.

Is Optimum Nutrition Serious Mass Worth It?

There’s an argument to be had that it’s more economical to have your weight gain, high-calorie needs met with a mass gainer. For example, if the average cost to buy a 1,200-calorie meal is around $20, you can save a lot of money using a mass gainer for some of your calorie needs since it only costs around $5-7 per serving for this 1,200-calorie protein powder. 

RELATED: 11 Best Supplements for Muscle Growth 2024

A person dumps a huge scoop of Optimum Nutrition Serious Mass into a shaker cup

That said, one full serving provides a whopping 2.5 cups of powder, which can be overwhelming for most and means there are very few servings per tub, so you would need to dig into your pockets often if you plan on using Serious Mass for long-term needs.  

Great for:

  • People with an already-healthy diet who need help boosting calories to gain muscle mass
  • Those already familiar and comfortable with the large scoop size of mass gainers
  • People who want something that tastes great with multiple flavors

Not recommended for:

  • People who don’t own a blender or prefer to use a shaker for their protein shake
  • Those who don’t like artificial colors, flavors, or sweeteners
  • Individuals on a tight supplement budget

Optimum Nutrition Serious Mass Specs

Price per serving$5.24 – $7.74
Serving size 2 scoops (340 grams)
FlavorsChocolate, Vanilla, Strawberry, Chocolate Peanut Butter, Banana
Calories per serving1,250-1,260
Protein content50 g
Carb content250-253 g
Fat content 5-6 g
Notable ingredientsMaltodextrin, whey protein concentrate, sucralose
Third-party tested?No

Experience Using Optimum Nutrition Serious Mass

Anthony had a generally good experience with ON Serious Mass, which is why he keeps going back to it. However, there were some issues with the lack of third-party testing, a slightly artificial flavor, and the price per serving. 

RELATED: Best Protein Powder for Weight Gain

Price Per Serving

This price per serving ranges from $5.24 to $7.74 depending on the container size you buy. Buying 16 servings provides the most value at $5.24 per serving, however buying only four servings lies on the higher end of the price range. This makes ON Serious Mass pretty expensive, especially since one serving only provides 50 grams of protein. 

RELATED: How To Make DIY Mass Gainer


The formulation of Serious Mass is relatively simple with the main ingredients being whey protein concentrate and maltodextrin. The remaining ingredients included are flavoring, artificial colors, sunflower/soy lecithin to help with solubility, and sweeteners. 

Looking down into a container of Optimum Nutrition Serious Mass

The first ingredient on the list is the one the product contains the most of by weight, which means that there is more maltodextrin than there is whey protein, but that is a common feature of mass gainers. 

RELATED: What to Look for in Protein Powder

That’s because carbs (in this case, maltodextrin) and protein (the whey concentrate) both have 4 calories per gram. To boost the calories in a weight gainer, it’s practical to include many grams of carbohydrates compared to protein because carbohydrates do not make you as full. There are up to 253 grams of carbs per serving in Serious Mass (the amount varies between flavors), but they would never be able to fit 253 grams of whey protein in one full serving. 

That said, there are only 50 grams of protein across all flavors of Serious Mass. So, it’s not recommended to rely on it as a primary protein source if you want muscle growth. Furthermore, whey protein concentrate is the cheapest type of protein and can contain as little as 35% of actual protein content by weight1.

Unlike whey protein isolate, whey protein concentrate’s processing is limited in that there is still a decent concentration of lactose and milk fat in the final product, which is a problem for those with lactose intolerance.

RELATED: Whey Protein Isolate vs Concentrate

Taste and Solubility 

Anthony rated Serious Mass 3.5 out of 5 stars in taste. He tried the vanilla flavor and had this to say: “To be honest, this is your typical artificial vanilla taste. It’s not offensive, personally, but it’s not anything to write home about either. On the bright side, it doesn’t overpower anything else you add to the shake (e.g., berries and flavorings).”

Side view of a shake next to a huge canister of Optimum Nutrition Serious Mass

He also gave it a 4 out of 5 in solubility. ON recommends using a blender with 24 ounces of fluid for 30 to 45 seconds, rather than the ubiquitous shaker bottle, and Anthony seconds this tip. “Well, it’s two large scoops, so it’s soluble so long as you’re using a blender,” Anthony notes. “No big lumps, but it does take some blending to get it all mixed.”

Side Effects

Whey protein is not known to cause serious side effects when taken as directed. With high protein dosages, though rare, several side effects may occur, including changes in bowel movement, acne, nausea, thirst, bloating, sleep problems, and headaches. In general, however, protein powder containing whey or milk is very safe, unless you have allergies to those ingredients. 

RELATED: Whey Protein Side Effects

Third-Party Testing 

Though most of Optimum Nutrition’s other supplements, such as their Gold Standard whey protein, are third-party tested by Informed Choice, there is no indication on the labeling or the website that Serious Mass Weight Gainer shares the same credentials. So, we rated it 2 out of 5 in this category. 

Comparison to Dymatize Super Mass Gainer  

Dymatize Super Mass Gainer

Dymatize Super Mass Gainer

GGR Score: 4.7 starstarstarstarstar

Product Highlights

  • Formulated with fast- and slow-absorbing, high-quality protein blends
  • Each serving provides 1,200-1,310 calories (depending on flavor)
  • Each serving contains 52 g of protein, 245 g of carbs, and 14 vitamins and minerals
  • Can be used to bake with
  • Banned substance-tested
  • Formulated to gain mass quickly
  • Available in two flavors: Rich Chocolate and Gourmet Vanilla

Pros & Cons


  • Banned substance-tested
  • Added vitamins and minerals
  • Fast- and slow-absorbing protein blends
  • Tastes good
  • Includes BCAAs


  • Requires 2.5 cups of powder for one serving
  • Thick
  • High sugar content
  • Contains sucralose

Bottom Line

High in calories, carbohydrates, and protein, Dymatize Super Mass Gainer could be a choice for those who do not mind large servings or artificial ingredients.

We have tried Dymatize Super Mass Gainer in the past and it has a very similar serving size, calorie count, protein, and carb content compared to ON Serious Mass. However, the ingredient list is much longer.

Dymatize also contains a protein blend that includes whey concentrate, isolate, and even casein, which isn’t necessarily superior to the whey concentrate in ON considering we don’t know the quantities. Both will still offer a similar profile of BCAAs. Dymatize also contains creatine monohydrate, but there is only 1 gram of creatine per serving, which makes it basically useless. 

Dymatize is also third-party tested for banned substances by Informed Choice despite being much more affordable per serving, but offers fewer flavors. 

Optimum Nutrition Serious MassDymatize Super Mass Gainer 
Price per serving$5.24-$7.74$3.91-$4.34
Serving size 2 scoops (340 g)2.5 cups (333 g)
FlavorsChocolate, Vanilla, Strawberry, Chocolate Peanut Butter, BananaVanilla, Chocolate
Calories per serving 1,250-1,2601,280
Protein content50 g52 g
Carb content250-253 g245 g
Fat content 5-6 g10 g
Notable ingredientsMaltodextrin, whey protein concentrate, sucraloseMaltodextrin, Protein Blend (whey protein concentrate, milk protein concentrate, whey protein isolate, whey protein hydrolysate, micellar casein), creatine monohydrate, sucralose
Third-party tested?NoYes, Informed Choice

Customer Experience 

If you’d like to return your product for a refund, you must return it within 30 days of purchase and it must have been ordered directly from ON or it won’t be accepted. If you need further support, you can use the live chatbot on the website or send an email to oncustsuppus@optimumnutrition.com.

A hand carefully lifts a scoop of powder from a container of Optimum Nutrition Serious Mass

Ordering Optimum Nutrition Serious Mass

When ordering ON Serious Mass from the Optimum Nutrition website, there is no subscribe and save feature, which is a bit of a bummer considering how few servings are offered per tub. Free shipping is available for orders over $75, so buying a 16-serving container would qualify.

Customer Reviews

On Optimum Nutrition’s website, ON Serious Mass has 4.8 out of 5 stars based on 169 reviews, with most reviews proclaiming that it’s a great product that tastes great and is effective at muscle building. 

On Amazon, the product has 4.5 out of 5 stars based on 66,311 reviews. Amazon reviewers also comment on the product’s effectiveness at helping them gain muscle mass, but there were mixed reviews on the flavor with many commenting they add peanut butter to help with the taste. 

Final Verdict of Our Optimum Nutrition Serious Mass Review

A mass gainer is different from the high quality protein you may take post-workout to help with muscle recovery, as it should be used to boost calorie intake on top of a high caloric diet. The grams of carbohydrates, content of BCAAs, and calorie count in ON Serious Mass can definitely accomplish this. 

That said, though Serious Mass is a great product in a number of ways, it can be very expensive if you plan to use it regularly. Those new to mass gainers may also be overwhelmed with the size of the scoops and it’s important to note that the supplement is not third-party tested. 

  • Great tasting and effective at muscle building, according to customer reviews
  • Can be used post-workout due to BCAA content as well as to boost calorie intake
  • Not third-party tested and should be used sparingly if on a tight budget

Full Rating

Optimum Nutrition Serious Mass

If you do not mind artificial ingredients, Optimum Nutrition Serious Mass is a good-tasting weight gainer with an impressive 1:5 protein to carbohydrate ratio.

Product Brand: Optimum Nutrition

Product Currency: $

Product Price: 39.99

Product In-Stock: InStock

Editor's Rating:

Optimum Nutrition Serious Mass Rating

Price per serving – 3.5
Formulation – 4
Taste – 3.5
Solubility – 4
Side effects – 5
Third-party testing – 2
Customer service – 5
Customer reviews – 4.8
Buy Now

Optimum Nutrition Serious Mass: FAQs

Does Optimum Nutrition Serious Mass work?

Providing over 1,200 calories, Serious Mass can help those who identify as a “hard gainer” to gain weight quickly.

What are the side effects of Optimum Nutrition Serious Mass?

Taking Serious Mass in moderation along with a healthy diet filled with whole foods has no serious side effects.

Can I take Optimum Nutrition Serious Mass daily?

Serious Mass can be taken every day as long as you meet recommended dietary requirements. 

Since Serious Mass offers minimal nutrients, using it as the majority of your daily calories can lead to nutrition deficiencies.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any diseases.


  1. Carunchia Whetstine ME, Croissant AE, Drake MA. Characterization of dried whey protein concentrate and isolate flavor. J Dairy Sci. 2005;88(11):3826-3839. doi:10.3168/jds.S0022-0302(05)73068-X 

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