Biologics and methotrexate carry similar rates of serious adverse events overall, and neither is categorically safer than the other. The answer depends on which specific risks matter most to you: liver strain, infection, daily side effects, or plans for pregnancy. Newer biologics targeting specific immune pathways do appear to have a meaningful edge in certain areas, particularly serious infections, while methotrexate causes more day-to-day gastrointestinal misery.
Serious Side Effects Are Similar Overall
A systematic review published in the Journal of General Internal Medicine compared methotrexate alone against several biologic classes, both as standalone treatments and in combination. Across every comparison, no significant differences emerged in rates of serious adverse events or in the number of people who had to stop treatment because of side effects. This held true for TNF inhibitors like adalimumab, certolizumab, etanercept, and infliximab, as well as non-TNF biologics like abatacept, rituximab, and tocilizumab. The pattern was consistent: when researchers looked at people dropping out of trials due to toxicity, the numbers were essentially the same regardless of which drug they were taking.
This doesn’t mean the drugs cause the same problems. It means the overall burden of serious harm is roughly equivalent. The types of risks differ, and that distinction matters when choosing between them.
Newer Biologics Have Lower Infection Rates
Infection risk is one area where a clear difference has emerged, at least for newer biologic classes. In a large study of psoriasis patients followed for a median of 4.8 years, biologics targeting IL-12, IL-23, and IL-17 were associated with a 35% lower rate of serious infections compared to periods when patients weren’t on these medications. Their infection rate was 1.4 per 100 person-years.
Methotrexate users, by contrast, had 2.7 serious infections per 100 person-years. TNF inhibitors fell in between at 2.2. Notably, methotrexate showed no statistically significant change in infection risk compared to being off treatment entirely, and the same was true for TNF inhibitors. The newer biologics were the only class that demonstrated a genuinely protective effect.
One important outlier: tofacitinib, a JAK inhibitor sometimes grouped with biologics, had an infection rate of 8.9 per 100 person-years, more than three times higher than methotrexate. Not all targeted therapies are equal on this front.
Methotrexate Is Harder on the Liver
Methotrexate’s most distinctive safety concern is liver toxicity. Between 15% and 50% of patients on long-term, low-to-moderate doses develop elevated liver enzymes, though these increases are usually mild and resolve on their own. About 5% see elevations more than double the normal range. Routine liver biopsies in long-term users show that roughly 30% develop mild-to-moderate tissue changes like fat deposits or low-grade inflammation, and somewhere between 2% and 20% develop some degree of liver scarring.
The good news is that modern dosing practices, typically 5 to 15 mg once weekly with folic acid supplementation, have made clinically significant liver disease rare even with years of use. But the monitoring burden is real. You’ll need liver function tests and complete blood counts every two to four weeks for the first three months, tapering to every 8 to 12 weeks, then every 12 weeks indefinitely. Several biologics, including adalimumab, etanercept, certolizumab, and abatacept, require no routine liver or blood count monitoring at all when used alone.
Methotrexate Causes More Daily Side Effects
About one in three methotrexate users (34.5%) develops enough gastrointestinal symptoms to qualify as intolerant. Among those intolerant patients, nausea affects 85.5%, stomach pain hits 59%, and vomiting occurs in 43%. These aren’t rare complaints. Many people describe a predictable cycle of feeling sick for a day or two after their weekly dose.
Biologics can cause injection-site reactions, headaches, or upper respiratory symptoms, but they generally don’t produce the same weekly pattern of nausea and fatigue. For quality of life between doses, most people find biologics easier to tolerate.
Cancer Risk Appears Comparable
Lymphoma risk has been a longstanding concern with both drug classes, but the data is reassuring. A large cohort study of rheumatoid arthritis patients over 65 found that biologics carried a hazard ratio of 1.11 for lymphoma compared to methotrexate alone, a difference that was not statistically significant. A separate study following over 19,500 patients across nearly 90,000 person-years of follow-up found an adjusted odds ratio of 1.0 for lymphoma in TNF inhibitor users versus non-users, and adding methotrexate to a TNF inhibitor didn’t increase the risk further.
The underlying inflammatory disease itself, particularly rheumatoid arthritis, raises lymphoma risk independent of any medication. Rare case reports have linked TNF inhibitor antibodies to an extremely rare and fatal type of lymphoma called hepatosplenic T-cell lymphoma, primarily in inflammatory bowel disease patients also taking thiopurines. But at a population level, neither biologics nor methotrexate appears to carry a meaningfully higher cancer risk than the other.
EULAR’s 2024 guidance on treating inflammatory arthritis in patients with a history of cancer does flag JAK inhibitors and abatacept as drugs to use with more caution, suggesting these specific agents may warrant extra consideration. Other biologics and methotrexate are not singled out in the same way.
Pregnancy Planning Changes the Equation
Methotrexate is definitively unsafe during pregnancy. It must be stopped at least three months before conception, and some guidelines consider one month acceptable under certain circumstances. This applies to both men and women.
Several biologics offer a significant advantage here. TNF inhibitors like infliximab, adalimumab, and golimumab can be continued throughout pregnancy when clinically needed. Certolizumab, which has minimal placental transfer, is considered compatible with the entire pregnancy. Etanercept is generally used through week 32, and sometimes beyond. If you’re planning a family, biologics give you far more flexibility to keep your disease controlled without harming a developing pregnancy.
Combination Therapy Doesn’t Double the Risk
Many treatment plans use both a biologic and methotrexate together, which naturally raises the question of compounding side effects. Data from the BIOBADADERM registry, covering over 2,800 patients and nearly 13,000 patient-years of follow-up, found that combining a biologic with methotrexate did not significantly increase the overall risk of adverse events or serious adverse events for any biologic class. Infection rates also remained stable in combination therapy.
The one exception was gastrointestinal side effects: TNF inhibitors combined with methotrexate produced 2.5 times more GI problems than TNF inhibitors alone. That’s consistent with what we know about methotrexate’s stomach-related effects.
There’s also a cardiovascular benefit to the combination. In a pooled analysis of over 88,000 patients on biologics, adding methotrexate was associated with a 24% reduction in the risk of heart attack, stroke, and cardiovascular death. This suggests the two drug classes may work synergistically to reduce the inflammation that drives heart disease in people with chronic inflammatory conditions.
How to Think About the Tradeoffs
Methotrexate is cheaper, well-studied over decades, and effective for many people. Its downsides are predictable: weekly nausea for a significant minority, regular blood draws to watch the liver, and a hard stop if pregnancy is on the horizon. Biologics cost more and require injections or infusions, but newer classes appear to carry lower infection risk, cause fewer daily side effects, and offer more flexibility around pregnancy. The overall rate of serious harm is similar between the two.
Your specific situation matters more than any general ranking. Someone with liver disease would lean toward biologics. Someone planning a pregnancy in the next year has a strong reason to avoid methotrexate. Someone whose disease responds well to methotrexate with minimal side effects has little safety-based reason to switch. The choice is less about which drug is universally safer and more about which risk profile fits your life.