Evenity (romosozumab) causes joint pain and headaches more often than any other side effects, affecting roughly 8 to 13% and 5 to 7% of patients respectively in clinical trials. Most side effects are mild, but Evenity also carries a serious cardiovascular warning that anyone considering the drug should understand before starting treatment.
Most Common Side Effects
In two large clinical trials involving more than 5,600 women receiving Evenity, the side effects reported at rates of 2% or higher were:
- Joint pain: 8.1% to 13.1% of patients, depending on the study
- Headache: 5.2% to 6.6%
- Muscle spasms: 3.4% to 4.6%
- Swelling in the hands or feet: 1.7% to 2.4%
- Fatigue or weakness: 2.3% to 2.5%
- Neck pain: 1.7% to 2.2%
- Insomnia: 1.7% to 2.0%
- Tingling or numbness: 1.4% to 2.0%
These numbers are worth putting in context. In the placebo-controlled trial, women receiving a dummy injection reported joint pain at 12.1% compared to 13.1% in the Evenity group. Headaches occurred at 5.8% with placebo versus 6.6% with Evenity. So while these side effects are real, the gap between the drug and placebo is relatively small for most of them. Many of these symptoms may reflect the population being treated (postmenopausal women with osteoporosis) rather than the drug itself.
Injection Site Reactions
Evenity is given as a monthly injection under the skin, typically two shots per visit (one in each prefilled syringe). About 4.9% of women in clinical trials experienced some kind of reaction at the injection site, compared to 2.8% in control groups. The most common complaints were pain at the site (1.7%) and redness (1.4%). These reactions are generally mild and short-lived.
In rare cases, more significant skin reactions can occur. At least one published case report describes a patient who developed large, inflamed, swollen plaques around the injection area after her first dose, even without any history of allergies. This type of severe skin reaction is uncommon but worth being aware of, particularly after your first injection.
The Cardiovascular Warning
The most serious concern with Evenity is its FDA black box warning about cardiovascular risk. This is the strongest type of safety warning a drug can carry. In one of the pivotal trials (the ARCH study), patients taking Evenity had a higher rate of heart attacks, strokes, and cardiovascular death compared to those taking alendronate, another osteoporosis medication.
The biological explanation ties back to how the drug works. Evenity blocks a protein called sclerostin, which normally slows bone formation. Blocking sclerostin activates a signaling pathway that rapidly builds new bone, which is exactly what you want for severe osteoporosis. The problem is that this same pathway plays a role in keeping blood vessels healthy. Sclerostin appears to have a protective effect against calcium buildup in artery walls. When you block it, you may inadvertently remove some of that vascular protection.
This concern is especially relevant for people who already have risk factors for heart disease, including kidney disease, diabetes, or a prior history of heart attack or stroke. For patients without cardiovascular risk factors, the absolute risk appears to be low, but the warning exists because the signal was real in clinical data.
Low Calcium Levels
Because Evenity stimulates rapid new bone formation, it pulls calcium from your bloodstream into your bones. This can cause hypocalcemia, or abnormally low blood calcium. Symptoms of low calcium include muscle cramps, tingling in the fingers or around the mouth, and in severe cases, heart rhythm changes. Your calcium and vitamin D levels need to be adequate before starting treatment, and supplementation is typically part of the regimen throughout the 12-month course.
Rare but Serious Bone Complications
Two bone-related complications that come up with many osteoporosis drugs are jawbone deterioration (osteonecrosis of the jaw) and unusual thighbone fractures (atypical femoral fractures). In the ARCH study, which evaluated over 4,000 patients, there were zero confirmed cases of either complication. This is reassuring, though both conditions are extremely rare even with long-term use of other osteoporosis medications, and Evenity is only used for 12 months. The short treatment window likely contributes to the very low risk.
Why Treatment Stops at 12 Months
Evenity is limited to 12 monthly doses. This isn’t just a recommendation; the bone-building effect of the drug diminishes over time as the body adapts. Continuing beyond 12 months isn’t expected to provide additional benefit. After completing the course, bone density gains begin to reverse unless you transition to a different type of osteoporosis drug, typically one that slows bone breakdown rather than building new bone.
Some patients may be candidates for a repeat course of Evenity after spending a year or more on a follow-on therapy, though this approach is considered on a case-by-case basis. The key point is that Evenity is designed as a jumpstart for bone density, not a long-term maintenance treatment, and the limited duration also limits your total exposure to the drug’s side effects.
How Evenity Compares to Other Bone Builders
The other major bone-building osteoporosis drug is teriparatide (Forteo), which works through a completely different mechanism. Forteo’s most commonly reported side effects include general pain, nausea, dizziness, and hair loss, with bone pain affecting about 7.6% of users. Joint pain and headaches, which dominate the Evenity side effect profile, are not among the top complaints with Forteo. Forteo does not carry a cardiovascular black box warning, but it does have its own warning about bone tumors based on animal studies, though this has not been confirmed in humans.
The choice between these two drugs typically depends on your fracture risk level, cardiovascular history, and how quickly bone density needs to improve. Evenity tends to build bone density faster, but the cardiovascular concern makes it a more careful decision for people with heart or vascular risk factors.