Did you know that if you go to the gym and work out, you are more likely to be abusing these very common supplements? It’s true, says new research, and some people have become hospitalized as a result.

We recently reported on a new study indicates that workout supplements, even legal ones that have been deemed relatively safe and effective by regulators like protein powder and creatine, are often being abused by unwitting individuals who don’t realize they’re harming their bodies — but exactly which ones and what makes them so harmful?

According to an NPR report, common whey protein powders, creatine supplements, and L-carnitine could place you at risk, according to a study published at the American Psychological Association’s annual convention. It involved 195 men who visit the gym at least twice a week and are between 18 and 65 years of age. It found that 40 percent of participants increase their use of supplements as time went on, 22 percent replaced meals with them, 8 percent were advised by doctors to cut back, and 3 percent had to be hospitalized. But what are the effects of these supplements?

Whey protein powder is a mix of globular proteins isolated from the liquid by-product of cheese production: whey. It is a good way to dramatically increase protein consumption, which is key to muscle growth. However, high does can have some short-term digestive issues or result in fatigue and headache, and too much protein consumption over a long period of time can cause a severe strain on the kidneys as they must handle a lot of extra waste products called ketones.

Then there’s creatine, which has a bit of a longer rap sheet when it comes to suspected health issues. Creatine is a nitrogenous organic acid that supplies energy to the cells in the body, especially for the muscle cells, making it popular among body builders and athletes who want to gain muscle mass. However, its health effects with too much consumption can be quite bad: kidney damage has been reported, as well as damage to the liver.

So when you take these supplements, just remember: moderation is key, as with everything, and always consult your doctor.