The most dangerous side effects of Entresto (sacubitril/valsartan) are angioedema, severe drops in blood pressure, kidney damage, dangerously high potassium levels, and fetal harm during pregnancy. Entresto carries a boxed warning, the FDA’s most serious safety label, specifically for its risk to unborn babies. Most people tolerate the medication well, but the serious reactions deserve attention because some can be life-threatening if missed.
Angioedema: The Rarest but Most Dangerous Reaction
Angioedema is rapid swelling beneath the skin, typically affecting the face, lips, tongue, or throat. When it involves the tongue or airway, it can block breathing and become fatal. This is the side effect that most distinguishes Entresto from older heart failure drugs, because one of its two active components slows the breakdown of substances in the body that can trigger swelling.
In the large PARADIGM-HF clinical trial, angioedema occurred in about 0.5% of patients taking Entresto, compared to 0.2% taking the older drug enalapril. That’s a low overall number, but the risk is not evenly distributed. Black patients had a notably higher rate of 2.4% on Entresto, compared to 0.5% on enalapril. The reason for this disparity isn’t fully understood, but it’s consistent with higher angioedema rates seen across medications that affect the same blood pressure pathways.
Switching timing also matters. Patients who recently stopped an ACE inhibitor before starting Entresto, particularly within 14 days, had roughly double the risk of angioedema compared to those who started fresh. This is why a mandatory 36-hour washout period is required after stopping any ACE inhibitor before your first dose of Entresto. The two drug types should never overlap.
Low Blood Pressure
Entresto lowers blood pressure by design, but in some patients it drops too far. In PARADIGM-HF, 11.1% of patients experienced symptomatic hypotension, meaning blood pressure low enough to cause dizziness, lightheadedness, or fainting. Another 16% had low readings on monitoring without feeling symptoms. That makes hypotension the most common serious side effect by sheer numbers.
You’re at higher risk if you’re dehydrated, on a low-salt diet, or taking high doses of diuretics (water pills). The typical approach is to address those factors first rather than stopping Entresto, since the drug’s heart failure benefits are significant. About half of patients in both the Entresto and comparison groups needed at least one dose reduction or temporary pause due to blood pressure issues during the trial, so adjustments are a normal part of treatment rather than a sign something has gone wrong.
Symptoms to watch for include feeling faint when standing up, persistent dizziness, or blurred vision. These tend to be most common in the first few weeks or after a dose increase.
Kidney Function Decline
Entresto affects the same hormonal system your kidneys rely on to regulate blood flow, so it can reduce kidney function in susceptible people. This is especially true for patients whose kidneys are already compromised or who have narrowing of the arteries that supply the kidneys (renal artery stenosis). In rare cases, this can progress to acute kidney failure.
Your doctor will check kidney function through blood tests before you start Entresto and periodically afterward, particularly after dose increases. Current guidelines consider an eGFR below 30 (a measure of how well your kidneys filter waste) a contraindication to starting the drug. If kidney function drops significantly while you’re on it, the dose is typically reduced or temporarily paused.
High Potassium Levels
Entresto can cause potassium to build up in your blood, a condition called hyperkalemia. Your heart depends on potassium staying within a narrow range, and levels that climb too high can cause dangerous irregular heart rhythms. Potassium above 5.5 mmol/L is the threshold where your prescriber will consider reducing your dose or pausing the medication. At 6.0 or above, the drug is stopped immediately and the situation is treated urgently.
People with existing kidney problems, diabetes, or those taking other medications that raise potassium (including certain diuretics and supplements) face the highest risk. Blood tests to check potassium are part of the standard monitoring schedule before starting and throughout treatment.
Fetal Harm During Pregnancy
Entresto’s boxed warning states plainly that the drug can injure and kill a developing fetus. The risk is highest during the second and third trimesters, when the medication can severely reduce kidney function in the fetus. This can lead to too little amniotic fluid, which in turn causes underdeveloped lungs, skull and skeletal abnormalities, dangerously low blood pressure in the newborn, and death.
If you become pregnant while taking Entresto, the drug should be stopped as soon as possible. This warning applies to the entire class of medications that act on the renin-angiotensin system, not just Entresto specifically. Women of childbearing age are typically counseled about reliable contraception before starting treatment.
What Makes Side Effects More Likely
Several factors raise your overall risk of experiencing serious reactions:
- Dehydration or low salt intake amplifies the blood pressure drop, especially if you’re also taking diuretics.
- Kidney disease increases the likelihood of both worsening kidney function and high potassium.
- Switching from an ACE inhibitor without waiting the full 36 hours raises angioedema risk substantially.
- Being Black is associated with a higher rate of angioedema, roughly five times the rate seen in non-Black patients in clinical trials.
Entresto is started at a lower dose and increased gradually every two to four weeks to the target dose. This slow titration is specifically designed to let your body adjust and catch problems early. Blood work to monitor kidney function and potassium is a routine part of this process, not a sign of concern. Most side effects that do emerge are manageable with dose adjustments rather than stopping the medication entirely.