JAK inhibitors: what they do and what to watch for

JAK inhibitors are pills that block Janus kinase enzymes inside cells. You’ve probably heard names like tofacitinib, baricitinib, upadacitinib, or ruxolitinib. Doctors prescribe them for immune-driven problems such as rheumatoid arthritis, psoriatic arthritis, ulcerative colitis, alopecia areata, and some blood disorders.

How JAK inhibitors work

These drugs stop signals that tell immune cells to cause inflammation. Picture cytokines as messages and JAKs as mail carriers. Block the carrier, and fewer inflammatory messages get delivered. That usually lowers pain, swelling, and tissue damage. Some JAK drugs hit multiple pathways, which can make them effective but also raise the chance of side effects.

Who uses them and what to expect

Your doctor may offer a JAK inhibitor when standard treatments like methotrexate or biologic injections don’t work or cause problems. You’ll start at a set dose, return for regular blood checks, and expect gradual improvement over weeks to months. Don’t stop the drug suddenly — talk to your provider first.

Common benefits include fewer swollen or painful joints, better control of flare-ups in ulcerative colitis, and hair regrowth reported in some people with alopecia areata.

Key risks and tests: because these drugs affect the immune system, infections are the main concern. Before starting, most doctors test for tuberculosis and hepatitis and run baseline blood tests: CBC, liver enzymes, and lipids. Expect repeat blood work during treatment. Shingles (herpes zoster) is more common on JAK inhibitors, so vaccination before treatment helps. Avoid live vaccines while on therapy.

Watch for serious signs: fever, persistent cough, sudden shortness of breath, or unexplained bruising. Some studies show a higher clot risk in older patients or those with heart disease. You may also see changes in blood counts, liver tests, or cholesterol.

Tofacitinib is mainly broken down by CYP3A4, so certain drugs can change its levels. Baricitinib is cleared mostly by the kidneys and may need dose changes if your kidneys don’t work well. Always tell your clinician about other meds, supplements, and herbal products.

Compared to biologic injections, JAK inhibitors are pills many people prefer. They can work quickly but still need lab checks and follow-up. Insurance and costs vary — prior authorization is common. Bring current meds and any infections to appointments. Keeping a simple symptom diary (pain, fatigue, fevers) helps your doctor decide if the drug is working or causing trouble. Talk openly with your care team today.

If you’re pregnant, planning pregnancy, or breastfeeding, discuss options before starting. With the right screening, monitoring, and clear communication with your healthcare team, JAK inhibitors can be a helpful option when other treatments don’t do the job.