Long-Term Side Effects of Propranolol in Infants: Key Points

Propranolol has been the go-to treatment for problematic infantile hemangiomas since its effectiveness was discovered by accident in the late 2000s, and the accumulating evidence on long-term outcomes is broadly reassuring. Large population studies and follow-up research have not found lasting neurological, cognitive, or growth-related harm in children treated during infancy. That said, the drug does carry real risks during treatment, and a few concerns deserve closer attention than they sometimes get.

Why Parents Worry About the Brain

Propranolol is lipophilic, meaning it dissolves readily in fat and crosses from the bloodstream into the brain more easily than water-soluble beta-blockers like atenolol.¹ Because treatment typically starts in the first months of life, when the brain is developing rapidly, parents understandably want to know whether early exposure could affect their child’s thinking, language, or behavior down the road.

The largest study on this question matched over 10,000 propranolol-treated children against controls and found no increased risk of ADHD, autism spectrum disorder, or speech-sound disorders. In fact, propranolol-treated children had a somewhat lower incidence of behavioral-emotional disorders, specific learning and developmental delays, and language disorders.² That finding held even in a subgroup of children who started treatment later, ruling out the explanation that earlier treatment simply reflected more attentive medical care.

A separate study directly compared neurocognitive functioning in children who had been treated with propranolol versus those treated with atenolol (which enters the brain far less). The two groups performed similarly on cognitive testing, supporting the conclusion that propranolol does not cause detectable long-term cognitive harm.³ Taken together, the neurodevelopmental picture looks encouraging, and parents can feel reasonably confident on this front.

Sleep Disruption During Treatment

One of the most common complaints parents report while their baby is on propranolol is sleep trouble. Because the drug reaches the brain easily, it can affect sleep architecture. A cohort study tracking infants at six months of age found that propranolol-treated babies had lower sleep efficiency and a trend toward more nighttime awakenings compared to untreated infants. Their total 24-hour sleep, however, was not affected, and subjective sleep quality and behavioral development scores remained normal.⁴

Clinicians have also reported agitation and restlessness in some propranolol-treated infants.⁵ These sleep-related effects seem to resolve once treatment ends. They are not trivial, though, especially for exhausted caregivers. If your baby’s sleep worsens significantly on propranolol, it is worth raising with the prescribing physician, as dose adjustments or timing changes sometimes help.

Hypoglycemia Is the Most Serious Acute Risk

Low blood sugar is the side effect that most worries pediatricians, because severe hypoglycemia in infants can, in rare cases, cause lasting neurological damage. Propranolol blocks the hormonal signals that help the body mobilize stored glucose during fasting, and infants have limited glycogen reserves to begin with. A Japanese post-marketing surveillance study estimated that severe hypoglycemia occurred in roughly half a percent of treated patients, with hypoglycemic seizures in about a third of a percent.⁶

Most children who experienced hypoglycemia recovered without lasting problems, but one patient in a published case series suffered severe brain damage and epilepsy. Several others turned out to have an underlying growth hormone deficiency that worsened their risk.⁷ The practical takeaway is that propranolol doses should not be given during illness when a baby is not eating well, and caregivers should know the signs of low blood sugar: unusual sleepiness, jitteriness, poor feeding, or pallor.

Some centers have adopted careful monitoring protocols with blood glucose checks during the initial dosing period. A prospective study of neonates starting propranolol under close monitoring found that blood glucose values remained normal in all patients, and no dose reductions were needed.⁸ This suggests that hypoglycemia is largely preventable with proper feeding schedules and vigilance during illnesses.

Does Propranolol Slow Growth?

Given that propranolol can dampen blood sugar responses and is taken during a period of rapid growth, it is natural to wonder whether treated children end up smaller. The short answer: they generally do not. One study followed children’s height and weight at three, six, and nine months into treatment and found no significant changes in growth indexes compared to pre-treatment measurements.⁹

A second study, however, found that children on propranolol for more than seven months showed some deviation in BMI-for-age and weight-for-age z-scores compared to World Health Organization norms, though neither group strayed from the normal weight range overall.¹⁰ The effect was subtle and stayed within what would be considered healthy, but it does suggest that longer treatment courses deserve ongoing growth monitoring. Animal research has also shown that propranolol itself does not reduce body size independent of nutrition, and bone-related blood markers like calcium and osteocalcin remain unchanged.¹¹

Breathing and Wheezing

Beta-blockers relax some types of smooth muscle but can tighten the smooth muscle in airways. In adults and older children with asthma, this is a well-known concern. In infants, the evidence is thinner but still worth knowing about. Case reports describe infants who developed wheezing for the first time while on propranolol for hemangiomas, an effect that is plausible given the drug’s mechanism.¹²

A more recent case report described an infant with a family history of asthma who developed new-onset bronchial asthma during propranolol therapy. The child’s asthma improved after propranolol was stopped, without any increase in asthma medication, strongly suggesting the drug was a contributing factor.¹³ Families with a strong history of asthma or allergies should discuss this risk with their doctor before starting treatment. And any infant who develops persistent coughing, wheezing, or labored breathing on propranolol should be evaluated promptly.

What Happens When You Stop Treatment

One concern that catches many parents off guard is rebound growth. After propranolol is discontinued, the hemangioma sometimes starts growing again. A retrospective study of over 400 patients found rebound growth in about 22% of cases, with the risk being similar whether the child was treated with propranolol or atenolol.¹⁴ Longer initial treatment courses were associated with a higher chance of rebound, which seems counterintuitive but may reflect that more persistent hemangiomas require longer treatment and are inherently more likely to regrow.

A separate study of over 300 patients treated for at least six months found a relapse rate closer to 13%, and noted that hemangiomas on the limbs were the least likely to rebound.¹⁵ The range in these studies tells you that rebound is not rare, but it also is not the majority outcome. When it happens, retreatment with another course of propranolol is usually effective.

Periocular Hemangiomas and Vision

Hemangiomas near the eye carry unique risks because they can press on the eyeball or droop the eyelid, potentially causing amblyopia (lazy eye) or astigmatism. Propranolol can shrink these lesions and reduce the pressure on the eye, but some visual problems may persist even after successful treatment. In one study of 17 children with periocular hemangiomas treated with oral propranolol, about 41% had amblyopia and about a quarter had significant astigmatism before treatment began.¹⁶ After propranolol shrunk the lesions, astigmatism improved in many patients, and vision equalized with patching therapy in nearly all of them.

A larger study of 30 patients confirmed that propranolol treatment led to a significant reduction in the hemangioma’s size and a measurable drop in cylindrical power (a measure of astigmatism) in the affected eye.¹⁷ The lesson here is that propranolol helps, but children with periocular hemangiomas still need long-term ophthalmological follow-up. Early treatment is better for vision outcomes, and patching for amblyopia may still be necessary even if the hemangioma responds well.

Mental Health at School Age

Beyond cognitive testing, researchers have also looked at broader mental health in school-aged children who were treated with propranolol as babies. A study of 105 children aged six to nearly twelve years assessed emotional and behavioral functioning, affect recognition, and quality of life. Neither propranolol-treated nor atenolol-treated children differed from each other on any mental health measure. Compared to population norms, these children scored normally on most quality-of-life scales, with slightly higher scores on autonomy and school environment.¹⁸ One area where parent-reported scores dipped was social support and peer relationships, though this finding likely reflects the visible scar or residual mark from the hemangioma itself rather than any drug effect.

How Propranolol Works Against Hemangiomas

Understanding the mechanism helps explain both why the drug is effective and where side effects come from. Propranolol was discovered to shrink hemangiomas essentially by accident, and the scientific understanding has been catching up since then.¹⁹ The drug works through at least three phases. In the first few days, it constricts the blood vessels feeding the hemangioma, which is why parents often notice the lesion looking paler almost immediately. Over weeks, propranolol blocks the signals that promote new blood vessel formation. Over months, it triggers the death of the blood vessel lining cells inside the hemangioma.²⁰

At a molecular level, propranolol suppresses key growth signals like VEGF and bFGF, which are the molecules hemangioma cells use to build and maintain their blood supply.²¹ Measurable drops in these molecules have been confirmed in the blood of treated infants after about a year of treatment.²² Interestingly, some research suggests propranolol’s anti-hemangioma effects go beyond just blocking beta receptors, as the drug also seems to affect vascular regression pathways through a separate mechanism involving a molecule called Ang2.²³

How Atenolol Compares

Atenolol, a water-soluble beta-blocker that enters the brain much less readily, has attracted interest as a potentially gentler alternative. A systematic review and meta-analysis comparing the two found that propranolol tended to have more adverse reactions and a slightly higher relapse rate than atenolol, but neither difference reached statistical significance.²⁴ Their effectiveness at shrinking hemangiomas was comparable. Both drugs also produced equivalent long-term neurocognitive outcomes and mental health profiles at school age, as mentioned above.

Atenolol is not yet as widely studied or universally available for this indication, and propranolol remains the standard first-line therapy in most guidelines. But for families concerned about sleep disruption or central nervous system effects, atenolol is an option worth discussing. The evidence is still maturing, and the choice between the two often comes down to physician preference and the specifics of the child’s situation.

Why Some Babies Respond Differently

Not every baby metabolizes propranolol at the same speed. The drug is broken down primarily by an enzyme called CYP2D6, and genetic variation in the gene encoding that enzyme affects how quickly propranolol is cleared from the body. One study found that infants with a particular genetic variant (G/G homozygotes at a specific CYP2D6 site) had the highest response rates to propranolol, while those with the C/C variant had the lowest.²⁵

Related research measuring actual propranolol blood levels confirmed that different CYP2D6 variants lead to different drug concentrations: some infants maintain higher blood levels of propranolol and its active breakdown products on the same dose.²⁶ This matters practically because a baby who metabolizes propranolol slowly may be more susceptible to side effects at a standard dose, while a fast metabolizer might need a higher dose for the same effect. Pharmacogenomic testing is not yet routine for this indication, but it may become more common as clinicians look for ways to personalize dosing.

A Side Effect You Might Not Expect

Here is one that rarely makes the list of standard warnings: dental caries. A case report described an 18-month-old who developed cavities in his upper front teeth while on propranolol solution for a hemangioma.²⁷ The cause was likely twofold: the liquid propranolol formulation contained sucrose as a sweetener, and propranolol itself can reduce saliva production through its beta-blocking action. Less saliva means less natural rinsing of the teeth, and sugary liquid sitting on emerging teeth is a recipe for cavities. Parents giving oral propranolol solution should ask about the formulation’s sugar content and consider wiping down their baby’s teeth or gums after each dose. Some pharmacies compound propranolol in sugar-free preparations, which may be worth requesting.

Monitoring During Treatment

Standard practice at most centers involves a cardiac evaluation before starting propranolol, including checking heart rate and rhythm. During the first dose and dose increases, heart rate, blood pressure, and blood glucose are typically monitored for several hours.²⁸ After the initial period, monitoring usually becomes less intensive, though caregivers are counseled to watch for signs of low blood sugar, wheezing, and excessive sleepiness.

Some families wonder whether topical propranolol (applied directly to the hemangioma as a cream or gel) avoids the systemic side effects. For superficial hemangiomas, topical formulations have shown effectiveness rates in the range of 78% to 90%, with only mild local skin reactions and no reported systemic side effects.²⁰ Topical treatment is not appropriate for deep or large hemangiomas, but for small, flat, superficial ones, it may offer a way to avoid the sleep, blood sugar, and airway concerns that come with systemic dosing. Availability and formulation vary by region, so this is another conversation to have with your child’s treatment team.