Adverse effects of binaural beats are rarely reported, although no safety trials have been conducted. Additionally, the frequency of binaural beats matters, and some may impair certain types  of cognition transiently. Of course, listening to beats too loudly can potentially damage hearing.
Although we did not find any research suggesting this, binaural beats could theoretically produce a negative effect in people with some sort of pre-existing neurological condition, simply due to the wide variety of possible interactions any intervention would have with diverse conditions.
There isn’t much safety data related to binaural beats, but they are likely safe. People with hearing or neurological conditions should exercise more caution.
Although the mechanism is still under investigation, it is thought that binaural beats elicit a “frequency following response” (FFR) , which is the tendency of the electrical activity in the brain to match the frequency of an external periodic stimulus such as a tone. This term is also referred to as “brainwave entrainment”.
By playing the perceived third tone at a certain frequency, the brain should (theoretically) increase the presence of brainwaves of the same frequency. Because different brain wave frequencies are associated with different types of mental activity, the binaural beat frequency could be used to improve certain types of cognition or produce specific moods. Some studies have successfully measured an FFR from binaural beats using electroencephalography (EEG), particularly when visual stimulation of the same frequency was used concurrently, although other studies have failed to find this effect.
Binaural beats may increase production of brainwaves of the same frequency, which could help facilitate certain aspects of cognition. Evidence is mixed, however.
There have been two studies that evaluated the efficacy of binaural beats on sleep, which have found some positive effects:
The first study, conducted in 21 people, found that using theta and delta binaural beats for 20 minutes prior to a nap had no effect on sleep latency (time to fall asleep), but did improve sleep stability (the regularity of the sleep-wake cycle) compared to silence.
The second study, conducted in 15 elite young soccer players, found that eight weeks of sleeping with binaural beats in the delta and theta range improved sleep and awakening quality, reduced daytime sleepiness, and improved mental state compared to silence.
Delta and theta binaural beats have shown some promise for improving some sleep parameters, but the jury is still out.
An uncontrolled study of 58 people  found that a 5 minute exposure to gamma binaural beats was sufficient to produce gamma waves in the brain, and that gamma waves measured during a long-term memory test were directly proportional to performance on that test, although binaural beats were not used during the test itself.
In a two-armed crossover study  of 32 people, participants received white noise preceding or following binaural beats 15 minutes prior to a memory task, and two minutes during. Half of the participants received theta beats and half received beta beats. Interestingly, the participants who listened to beta beats experienced improved free recall and word recognition, whereas those who listened to theta beats actually did worse. The researchers suggest that this may be because theta waves are associated with “states incompatible with the encoding of information” such as relaxation, decreased anxiety and activation, and increased hypnotic susceptibility.
A study of 34 people  compared the effects of silence, a pure 240 Hz tone, classical music, and binaural beats at 5, 10, and 15 Hz on a verbal working memory task, and saw that the 15 Hz (beta) beats significantly improved performance. 5 and 10 Hz beats had no effect.
Another study in 28 people  used the same experimental design, but instead tested visuospatial memory, and found 15 Hz produced a significant improvement in performance. Silence and 10 Hz beats produced the worst performance and the other interventions had an intermediate effect.
In a study of 24 participants, 40 Hz (gamma) binaural and monaural beats produced significantly better performance on reaction time in an attention test (the Flanker test), when compared to white noise. Overall performance was, however, not improved. There was no improvement in working memory, and no difference between those who received binaural and those who received monaural beats.
A uncontrolled study of 25 people  found that receiving binaural beats in the delta, theta, and alpha ranges while sitting in a massage chair had significantly reduced mental fatigue and improved attention, verbal short and long-term memory, and non-verbal long-term memory than those who received only massage.
Another uncontrolled study  investigated the effects of binaural beats plus visual stimulation in two groups of boys with learning disabilities. The first group had 14 participants and received two minutes of 10 Hz (alpha) beats, one minute of a constant tone, and two minutes of 18 Hz (beta) beats sequentially along withequivalent visual stimulation using red LED lights for 25 minutes, 80 times over eight weeks. This group saw improvements in one of two IQ tests used and better memory, reading and spelling compared to before the treatment. Additionally, parents and teachers in this group rated the students as having improved emotion, academic performance, and attention. The second group had 12 participants and underwent the same procedure, but for only 18 sessions over six weeks. This group saw improvements in verbal IQ and spelling.
In an uncontrolled crossover study of 29 participants, listening to 16 and 24 Hz (beta) beats masked by pink noise produced significantly increased detection and reduced false alarms on a vigilance task than did listening to 1.5 and 4 Hz (delta and theta) beats. Additionally, listening to theta and delta beats increased feelings of confusion, fatigue, and depression in response to the vigilance task compared to listening to beta beats. As previously mentioned, this may be related to the difficulty of engaging in cognitively demanding tasks when listening to theta and delta beats.
Beta and gamma binaural beats may improve working memory and various measures of cognition, although more research is required. Theta and delta beats might acutely reduce performance.
24 participants listened to white noise, 40 Hz gamma binaural beats or monaural beats while performing an attention test and a working memory test with two minutes between tests. The binaural and monaural beat groups performed better on both tests, and there was no difference between the binaural and monaural beat groups.
A study of 20 children and adolescents with ADHD  found that 20 minutes of beta beats, thrice weekly for three weeks did not improve any measures of attention compared to a sham treatment, although parents reported fewer homework problems.
In a study of 36 college students, gamma beats did not improve the suppression of irrelevant information during an attention task, but did increase visual attention compared to control.
There is some evidence (particularly with gamma frequencies) that binaural beats could improve ADHD, but so far the results are mixed and further research is required.
One study, conducted in 24 people, has investigated the effect of binaural beats on divergent (e.g., answering “how many ways can you use a piece of paper?”) and convergent (e.g., answering “what single word could be put in front of ‘market’, ‘star’, and ‘hero’?”) creativity.
This experiment exposed participants to alpha or gamma beats with white noise or a constant 340 Hz tone for 3 minutes prior and during a creativity task. Additionally, striatal dopamine levels were estimated using “eye-blink rates” (EBRs). Both alpha and gamma beats seemed to improve divergent thinking in people with low EBRs (<20 blinks/min), but actually impaired those with higher EBRs. The researchers suggest that those with low EBRs have low dopamine and have more room for improvement, or it could be because dopamine improves neural synchronization which helps people who are lower, but creates more noise for those who are sufficiently high.
A study of 40 college students  found that listening to gamma binaural beats while sorting two separate groups of numbers improved cognitive flexibility compared to those who listened to a 340 Hz tone. In this study, “cognitive flexibility” was measured as the ease with which participants moved from working with one group of numbers to another.
Creativity is a difficult concept to test, but a small amount of evidence suggests that gamma and alpha beats may improve it in some respects. One study suggested that baseline striatal dopamine levels will influence if you respond positively or negatively to treatment, so further research is required.
A study of 104 patients  undergoing elective surgeries found that receiving binaural beats using delta frequencies significantly reduced pre-operative anxiety compared to music alone or silence.
A trial of 64 college-aged students  found increased parasympathetic tone (as measured by heart rate variability) after exposure to theta beats, although there was no difference in reported stress levels compared to control.
In a study of 60 patients undergoing dental surgery,  alpha beats given immediately after local anaesthesia significantly reduced preoperative anxiety compared to control.
A study in 32 people  found that relaxing music paired with alpha binaural beats was more relaxing than the participant’s favorite music, as measured by blood pressure and heart rate, although it did not increase the presence of alpha waves as measured by EEG. A second part of the study saw that listening to the same relaxing music plus alpha beats for 30 minutes daily for a week could increase overall alpha wave production in the brain, but did not have any long-term effects on heart rate and blood pressure.
An uncontrolled study of 14 people  found that three minutes of exposure to theta, alpha, beta, or gamma beats did not alter EEG readings or produce changes in emotional arousal as measured by skin conductance and rate.
In a study of 15 young and 15 elderly people, meditative music paired with theta beats had a more relaxing effect in classical music in young people, but classical music was more relaxing in elderly people.
An uncontrolled study of 25 people  found that those receiving binaural beats in the delta, theta, and alpha ranges while sitting in a massage chair had significantly reduced mental fatigue and improved attention, verbal short and long-term memory, and non-verbal long-term memory than those who received only massage.
In a study of 21 individuals, 20 minutes of theta beats increased parasympathetic and decreased sympathetic activation post-exercise compared to control, as measured by heart rate variability.
A randomized controlled trial of 411 men undergoing diagnostic cystoscopy and/or ureteral-stent removal — under local anaesthesia — found that listening to 10 Hz (alpha) beats during the procedure lowered pain and anxiety ratings more than did listening to classical music or silence. It’s worth noting, however, that the tolerance for the binaural beats was significantly lower, with only 77% tolerating treatment in the binaural beats group versus 92% and 96% in the classical and silence groups.
A randomized controlled trial in 90 individuals undergoing dental surgery found that 10 minutes of 10 Hz (alpha) beats reduced preoperative anxiety about as well as droning, instrumental music tuned to 432 Hz. Although there were no differences between these two groups, they both reduced anxiety considerably compared to 10 minutes of silence.
Delta, theta, and alpha beats have been shown to reduce anxiety and improve parasympathetic tone. This effect is most consistent in preoperative patients, and may not be as effective in older adults.
In a study of 49 boys receiving propofol and caudal blockade  (epidural) for sub-umbilical surgery, delta beats were able to reduce the amount of propofol required for anaesthesia compared to control.
A crossover study of 17 people with chronic pain  found that one 30 minute session of theta beats in lab conditions plus unlimited use for one week reduced pain intensity, psychological stress, and analgesic use compared to a sham treatment.
In a study of 40 individuals  who underwent total knee replacement surgery, those who received delta beats prior to surgery used nearly 50% less morphine in their first postoperative day compared those listening to a constant 256 Hz tone.
In 36 adults with chronic pain, 20 minutes of theta beats daily for two weeks significantly reduced pain intensity compared to a sham treatment.
Theta and delta binaural beats seem to improve pain for individuals who have chronic pain or are undergoing surgery, although the few studies conducted thus far have been short-term in nature (measuring response either immediately or after two weeks).