Steroids work by entering your cells and changing which genes get turned on or off, which alters how your body handles inflammation, immune responses, or muscle growth depending on the type. The word “steroid” actually refers to two very different kinds of drugs: corticosteroids, which fight inflammation, and anabolic steroids, which build muscle. They share a similar basic chemical structure but do opposite things in your body.
Two Types of Steroids, Two Different Jobs
Corticosteroids are synthetic versions of cortisol, a hormone your adrenal glands produce naturally. Doctors prescribe them to reduce inflammation and calm an overactive immune system. Common examples include prednisone, hydrocortisone, and cortisone.
Anabolic steroids are synthetic versions of testosterone. They promote muscle growth and are legitimately prescribed for hormone deficiencies, but they’re more widely known for misuse among athletes and bodybuilders. Despite sharing the name “steroid,” these two drug classes act on different receptors and produce fundamentally different effects.
How Corticosteroids Shut Down Inflammation
Because corticosteroids are small, fat-soluble molecules, they pass through cell membranes easily and get inside cells fast. Once inside, they bind to a specific protein called the glucocorticoid receptor. This receptor acts like a switch: when the steroid attaches to it, the receptor changes shape, travels into the cell’s nucleus, and starts influencing which genes are active.
The key anti-inflammatory effect comes from blocking two molecular switches (called NFκB and AP1) that normally activate genes responsible for producing inflammatory signals. These signals include the chemical messengers that cause swelling, redness, pain, and heat. NFκB is present in nearly all immune cells and controls the production of inflammatory compounds, so shutting it down has a broad, powerful dampening effect on inflammation throughout the body.
Corticosteroids also suppress the overall immune response. This is why they help with autoimmune conditions where the immune system mistakenly attacks healthy tissue, and why they’re used to prevent organ rejection after a transplant. The tradeoff is that the same immune suppression can leave you more vulnerable to infections.
How Anabolic Steroids Build Muscle
Anabolic steroids work through a parallel but distinct pathway. They bind to androgen receptors inside muscle cells. Once activated, the receptor separates from helper proteins, pairs up with a copy of itself, and moves into the nucleus. There it attaches to specific stretches of DNA and ramps up the production of proteins needed for muscle fiber growth and repair.
But boosting protein production is only half the equation. Anabolic steroids also reduce muscle breakdown. They do this partly by blocking the glucocorticoid receptor (the same one corticosteroids activate), which prevents cortisol from triggering its normal muscle-wasting effects. They also suppress specific genes that would otherwise break down muscle protein. The net result is that your body builds muscle faster and loses it slower, shifting the balance strongly toward growth.
Several other growth-promoting processes get amplified as well, including the production of a growth factor called IGF-1 and the recruitment of satellite cells, which are the repair cells that fuse with damaged muscle fibers to make them larger and stronger.
What Corticosteroids Treat
The list of conditions treated with corticosteroids is long, precisely because inflammation plays a role in so many diseases. Oral forms like prednisone (typically prescribed at 5 to 60 milligrams per day depending on the condition) treat rheumatoid arthritis, lupus, inflammatory bowel disease, and severe allergic reactions. Inhaled corticosteroids manage asthma and nasal allergies by delivering the drug directly to the airways. Injections target localized problems like tendinitis or joint inflammation. Eye drops treat inflammatory eye conditions like uveitis.
Corticosteroids also treat Addison’s disease, a condition where the adrenal glands don’t produce enough cortisol on their own. In this case, the steroid replaces what the body can’t make rather than suppressing an overactive system.
Oral corticosteroids typically start working within about 2 hours, which makes them useful for acute flare-ups. Inhaled versions work more gradually and are designed for long-term control rather than immediate relief.
Why You Can’t Just Stop Taking Corticosteroids
One of the most important things to understand about corticosteroids is what happens when your body gets used to them. Your brain constantly monitors cortisol levels. When you take a corticosteroid, your brain detects the extra cortisol-like activity and responds by dialing down its signals to the adrenal glands. Over time, the adrenal glands actually shrink from disuse and lose their ability to produce cortisol on their own.
If you suddenly stop taking the medication, your body can’t make enough cortisol to compensate. This can trigger withdrawal symptoms or, in severe cases, a dangerous drop in cortisol called an adrenal crisis. This is why doctors taper the dose gradually, giving your adrenal glands time to wake back up and resume normal production. The longer you’ve been on corticosteroids, the slower the taper typically needs to be.
Side Effects of Long-Term Corticosteroid Use
Short courses of corticosteroids are generally well tolerated, but long-term use carries significant risks. Hypertension develops in more than 30% of long-term users. Bone fractures affect 21% to 30%, because corticosteroids accelerate bone density loss. The risk of developing type 2 diabetes is roughly four times higher than in people not taking these drugs. Other common problems include weight gain, elevated blood sugar, cataracts (1% to 3%), and gastrointestinal issues.
Psychiatric effects are also well documented. Some people experience mood swings, anxiety, insomnia, or even psychosis, particularly at higher doses. These side effects are a major reason doctors try to use the lowest effective dose for the shortest possible time.
Risks of Anabolic Steroid Misuse
Anabolic steroids carry their own set of dangers, particularly at the doses commonly used outside medical supervision. The cardiovascular effects are striking: HDL (protective cholesterol) drops sharply while LDL (harmful cholesterol) rises. Research from UCSF estimated that heart attack risk increases by 58% at a moderate dose of one common anabolic steroid, doubles at twice that dose, and triples at four times that dose.
Liver damage is another serious concern. Some users develop grade III or IV liver toxicity, categories that represent significant and potentially dangerous injury to liver tissue. Beyond these organ-level effects, anabolic steroid use can cause acne, hair loss, testicular shrinkage, infertility, and mood disturbances sometimes called “roid rage.” In women, masculinizing effects like voice deepening and facial hair growth can be irreversible.
The Shared Biology Behind Both Types
Despite their different purposes, both types of steroids follow a remarkably similar playbook at the cellular level. Both are fat-soluble molecules that slip through cell membranes. Both bind to an intracellular receptor that acts as a gene switch. Both cause that receptor to travel into the nucleus and change gene activity. The difference comes down to which receptor they target and, consequently, which genes get turned up or down.
Corticosteroids activate the glucocorticoid receptor and suppress inflammatory gene programs. Anabolic steroids activate the androgen receptor and boost muscle-building gene programs. In fact, anabolic steroids partly work by blocking the glucocorticoid receptor, which means the two drug types are, in a sense, working against each other at that particular receptor. This shared molecular logic is why both are called steroids, even though their effects on your body could hardly be more different.