Long-term effects of antihistamines on mind and CNS

Long-term effects of antihistamines on mind and CNS

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Can maybe someone share knowledge or guesses on the following questions:

  1. Does the prolonged use of antihistamines cause long-term effects on mind or CNS?

  2. Are there any known evidences of their influence of formation of CNS or personality when taken at a young age?

  3. Generation-II antihistamines are said to be next to devoid of sedative effects since they selectively block just the H1-receptors. However, they are reportedly potentially mind-altering. How is this possible?

How Over-the-Counter Sleep Aids Can Hurt Your Brain

Over-the-counter sleep aids are marketed as a safe, effective and non-habit-forming way to get some zzz’s when sleep seems hard to come by. But what are the long-term effects on your brain? We asked Dan Kaufer, MD, a neurologist and director of the UNC Memory Disorders Program.

Are over-the-counter sleep aids safe? What effects do they have on your brain?

There are three classes of medications that are notorious for causing cognitive side effects. The most common one is benzodiazepines, which includes Valium and Xanax. These are prescribed to treat anxiety and sometimes sleep. Drugs in this class are generally not recommended for long-term use as a sleep aid because they can impair memory and require higher doses over time to achieve the same effect. The other class of medications is narcotic analgesics. These are getting a lot of attention right now—like hydrocodone or oxycodone—because they are very addictive.

Another drug class people don’t realize may undermine brain health is antihistamines. They are commonly used to treat allergies and are generally safe. However, one of these drugs, Benadryl (diphenhydramine), is commonly used in over-the-counter sleep agents. Taking an over-the-counter sleep aid with diphenhydramine once in a while is generally not going to cause problems, other than a possible hangover the next day.

Older people, however, can get confused when taking diphenhydramine because it also blocks a brain chemical called acetylcholine, which plays a big role in attention and short-term memory. Taking diphenhydramine over a long period of time can actually predispose people to dementia. You should be careful not to use these types of medicines all the time in order to get good sleep.

Does that mean it’s not safe to take over-the-counter antihistamines to treat allergies? The pollen is everywhere, and I can’t stop sneezing!

There are different antihistamines, and Benadryl (or diphenhydramine) is among the worst in terms of cognitive side effects. Other types of antihistamines are used to treat allergies, but none of them are used in sleep aids. It’s important to find one that allows you to function well and control your allergy symptoms. The best way to do that is to consult your physician.

Why is a good night’s sleep so important to overall brain health?

One of the things we’re learning more about is that neurocognitive disorders arise from little perturbations in brain metabolism that lead to the gradual buildup of protein deposits over many years. Exposure to diphenhydramine over the short term can make older folks a little squirrely, but long-term use over many years may lead to Alzheimer’s disease.

If people are unable to achieve a good night’s sleep, they really need to consult with a physician. We’re learning more and more how important sleep is for not just short-term brain functioning, but for long-term brain functioning as well.

One of the current theories about what contributes to the development of neurodegenerative disorders is the accumulation of toxic substances in our brains over many years. We’ve learned that sleep plays a role in eliminating these toxic substances. One of the consequences of not getting enough sleep is that these substances stay in the brain and cause a little bit of damage, which, multiplied over many years, can lead to a neurodegenerative disorder.

So a good night’s sleep isn’t just important for how you do the next day, but not sleeping well over a long period of time can have very dire consequences.

Is there anything I can take safely if I’m having trouble getting sleep?

If sleep is a problem, there are several things people can do. There are other natural products people can take to help them get some sleep, such as melatonin. As far as we know, melatonin in general is a perfectly good substitute for diphenhydramine. It’s a natural supplement. It’s the chemical in the brain that actually induces sleep in a natural way.

If you’re having trouble sleeping, talk to your doctor about enrolling in a sleep study. We have locations in Chapel Hill or Wake County.

Effects of long-term and brain-wide colonization of peripheral bone marrow-derived myeloid cells in the CNS

Background: Microglia, the primary resident myeloid cells of the brain, play critical roles in immune defense by maintaining tissue homeostasis and responding to injury or disease. However, microglial activation and dysfunction has been implicated in a number of central nervous system (CNS) disorders, thus developing tools to manipulate and replace these myeloid cells in the CNS is of therapeutic interest.

Methods: Using whole body irradiation, bone marrow transplant, and colony-stimulating factor 1 receptor inhibition, we achieve long-term and brain-wide (

80%) engraftment and colonization of peripheral bone marrow-derived myeloid cells (i.e., monocytes) in the brain parenchyma and evaluated the long-term effects of their colonization in the CNS.

Results: Here, we identify a monocyte signature that includes an upregulation in Ccr1, Ms4a6b, Ms4a6c, Ms4a7, Apobec1, Lyz2, Mrc1, Tmem221, Tlr8, Lilrb4a, Msr1, Nnt, and Wdfy1 and a downregulation of Siglech, Slc2a5, and Ccl21a/b. We demonstrate that irradiation and long-term (

6 months) engraftment of the CNS by monocytes induces brain region-dependent alterations in transcription profiles, astrocytes, neuronal structures, including synaptic components, and cognition. Although our results show that microglial replacement with peripherally derived myeloid cells is feasible and that irradiation-induced changes can be reversed by the replacement of microglia with monocytes in the hippocampus, we also observe that brain-wide engraftment of peripheral myeloid cells (relying on irradiation) can result in cognitive and synaptic deficits.

Conclusions: These findings provide insight into better understanding the role and complexity of myeloid cells in the brain, including their regulation of other CNS cells and functional outcomes.

Keywords: Bone marrow transplant Brain CSF1R inhibition Irradiation Microglia Monocytes.


As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.


Took a look at the study
The diffence between the people that were in the non users and heavy users is massively different. 3x higher on EVERY risk factor stroke, obese, etc.. Odd this would get so much traction with the press.. Borderline irresponsible of Harvard to publish this on their blog. Nothing here even hints at causality

here is what the experts say. Also people have been taking bendryl for 70 years, over the counter for 30 years. If this was causing dementia the rates would be increasing..
Dr. Knopman said that it was “highly unlikely” that the drugs themselves were the direct cause of the dementia, adding that the ultimate underpinnings of the article have a strong biologic basis.
Anticholinergic drugs “affect the area of the brain that facilitates learning and memory, and that’s the basis of the cholinergic model of Alzheimer’s,” he said. “That pharmacologic profile probably has negligible impact on people under 60, but with people with incipient dementia, the drug probably exacerbates the symptoms.”
Dr. Knopman said the main limitation with a prospective study is an indication bias. He suggested that the use of these drugs might be because of incipient dementia, rather than the drugs themselves causing the dementia.

Trouble sleeping, especially past middle age?

Worth considering: your body makes as much melatonin as it needs but only starts to do it after the last blue light goes away in the evening — if you let it.

Blue light has a dark side – Harvard Health

You can find yellow “bug light” bulbs cheap, or amber “turtle safe” lights.

(The blue light ‘wakeful/attention’ switch is evolutionarily very, very old. Daytime sky light color — Florida protects baby turtles so they go toward the ocean instead of toward the freeway)
— or any automotive supplier has 12-volt “clearance” amber LED lights. Remember there’s a spike of blue in even “warm white” lights. You can see it.

That’s what drives the phosphor that emits the rest of the color.

Harvard University
May 1, 2012 – Light at night is bad for your health, and exposure to blue light emitted by electronics and energy-efficient lightbulbs may be especially so.

My mother has taken these drugs and she has made such a turnaround since being off of them that it amazes me…..

I’ve been taking diphenhydramine for three years, and have been noticing a definite decline in short-term memory and the ability to retrieve the word I need. Have been blaming it on the job being more stressful than it seems. Stopped taking it around Valentine’s Day when I first came across the info being discussed here. Have just in the past day or so noticed a little lifting of the fog, but I also take supplements specifically for brain, and meditate. Maybe has something to do with quicker recovery. Experience has shown me DHA has the most noticeable effect, at least at short-term. For brain I also take B Vites and ginkgo. So I don’t know that everyone would feel some recovery that quickly, or that I’ll recover completely. But I think I will, and will use my newly recovered mental powers to search out ways to enhance that recovery. So good luck all you’re on a computer here, won’t find a more convenient way to research what you need now.

May I just point out that this article, as presented, is meaningless.

54 percent increase FROM WHAT? Without knowing the relative distributions of people in control and non-control groups this tells us nothing.

Was the risk 1/100 increased to 1.5 in 100? Was it 25/100 increased to 37.5/100?

Learn how NOT to lie with statistics please…

Obviously, it was not 1/100 with an increase to 1.5/100. Far more than 1% of the population acquires dementia. You make a valid point though. I was thinking the same thing you were. If 17% of the population acquired dementia without taking the suspected drugs, and 26% of those who took the suspected drugs acquired dementia, it does lead to some suspicion though. Like you said, we need to see the exact numbers.

Hi, thanks for the informative research link. There is always the risk of any medication, and it is challenging to know which poses the greater risk-allergicic reaction, untreated depression, or insomnia.

I have read too that Melatonin is also not without risk as the hormonal effects for older folks causes problems, and that is best used as a short term reset for sleep disorders.

Gloves, face masks, good sleep hygiene, and increasing activities that improve our quality of life seem all the more necessary when faced with damage from the pharmacopeia approach to allergies, sleep disorders depression, and lack of physical conditioning. Just a thought.

Thanks for a great discussion

Recently I lost my COBRA coverage. It was very expensive but they kicked me out and the only insurance I could get is MediCal. Today I met my new primary care MD (newly minted Resident). I asked for a refill of oxazepam that I have taken for 15 years without any problem. The doctor did not want to fill it. He recommended melatonin, benadryl and Elavil. So he wanted to give me a combo of anitcholinergics. I told him I have tried each in the past with poor results. I also mentioned this research as a concern. His reply, “I have read the information”. End of discussion. He suggested I might need to find another doctor unless I want to take his Rx. Disappointing.

I believe I have an early s/s of dementia caused by the benadryl and I am scared to death at this point 2/24/15. I took 200mg Benadryl for allergies in Texas (lots, lots of allergies in TX) for about 15 years. The prescription was read, Benadryl 50mg po qid. My husband is a physician, and his friend who also is a physician whote the prescription for me after seeing an horrible allergy attack and the trip to the ER for anaphylactic episode. About 5 to 6 years later I started to noticed that I was forgeting names (but could see the face of the person in mind’s eye, just can’t bring the names up), often can’t find the things. I often don’t remember what I have done minutes before I start another project thus running the car in the garage for hours… it just wanted to warm up the car before take off but changed mind to do another project. I also left house while the eggs were boiling in the kitchen… when I came home after having a lunch with friends, the house was full of the smoke… I also not showing up at the dinner party which was for my honor. They said a week before and I agreed to be there.

My family has no history of dementia.
No one told me about long term use of the dementia effect from the Benadryl. I told my FPs & other specialists (when I see them for other reasons, but they do the medication inventory on new pt) they never questioned me taking such a high doeses of the Benadryl for all these years… now what should I do? I understand this is a permanent state. No way to cure it. Please help me.

What you are experiencing is not necessarily early signs of dementia. Talk to your husband more about this. I did similar things as you when I was in my twenties and thirties. I am not in my fifties and am not any worse. There can be many reasons for forgetting. Stress, fright, ADD, and medications to name a few, can all cause this to happen. I think 200 mg of benedryl is too much though. I have severe allergies myself. The allergist said I am one of his ten worst patients. I limit the benedryl to 25 mg a day though.

I’m a White Male age 77. I’ve been taking one Benadryl and 10 mg Melatonin for sleep for the last 27 years and haven’t noticed any dementia although I do read slower to fully comprehend what I read.

I have been taking Benedryl for years for insomnia. Occasionally I will take Ambien or Melatonin. I never take more than 1/2 tablet and probably average 2-3 Tylenol PM/Alieve PM a week. Any suggestions as to what to take instead? And, at 52 years, will there still be long term affects if I stop now?

Thank you for the informative article. I am worried about the medications my husband (age 81) is taking. Both over the counter (Advil PM, contains diphenylhydramine) and the prescription drugs you mentioned. He has complained about brain fog. Will double check all his medications for interactions and/or anticholinergic actions.

I have panic attacks and allergies and the best alternative to some drugs (xanax and 12/24hr. allergy pills that didn’t work). I have been taking Benedryl almost regularly for the past 5 yrs. I would take up to 4 doses a day during my allergy season and at least 1 or 2 doses every other day! My question is since I quit taking it about 2 wks ago…..will the effects be reversed or am I simply keeping the dimentia symptoms from coming on faster and harder or whatever. Will I get better and be back to me? Or am I screwed.

Avoiding the Long-Term Effects of a Concussion

Considering that one of the biggest risk factors for developing long-term symptoms after a concussion is suffering from multiple concussions, it is important to allow your brain time to heal. According to Jeffrey English, M.D ., a neurologist at Piedmont Healthcare, 80% to 85% of those suffering from a concussion (with the exception of professional athletes) recover within two to three weeks with no known long-term health consequences. Dr. English goes on to state that there is evidence that sustaining a brain injury when you haven’t fully recovered from a concussion can have long-term consequences.

It is for this reason that healthcare professionals require patients to abstain from normal physical activity until they meet certain requirements. Dr. English urges those who have suffered from a concussion to first complete a five-step progressive physical exertion plan with their physician before returning to regular activity. He also recommends that coaches, players, and parents keep an eye out for symptoms of concussion as a preventative measure against long-term effects in young athletes.

Finally, if you or someone you know is suspected of a concussion, don’t wait to seek medical attention. Regardless of whether or not you exhibit some of the most common signs of a concussion , it is important to get checked out after taking a hit to the head. Concussive symptoms can sometimes be elusive depending on the individual, so it is important to meet with a physician.

Sleep Issues

Long term usage of antihistamines have also been associated with lowering the immunity system and sometimes people with underlying diseases such as Herpes, HPV or HIV can make these conditions more severe.

Always consult a doctor when planning to take antihistamines and as a rule, never be on a drug for too long as its always best to not just treat the symptoms but understand what is causing it and preventing it or curing that. Long term usage of antihistamines is detrimental to one&rsquos health.

One in ten have long-term effects 8 months following mild COVID-19

Eight months after mild COVID-19, one in ten people still has at least one moderate to severe symptom that is perceived as having a negative impact on their work, social or home life. The most common long-term symptoms are a loss of smell and taste and fatigue. This is according to a study published in the journal JAMA, conducted by researchers at Danderyd Hospital and Karolinska Institutet in Sweden.

Since spring 2020, researchers at Danderyd Hospital and Karolinska Institutet have conducted the so-called COMMUNITY study, with the main purpose of examining immunity after COVID-19. In the first phase of the study in spring 2020, blood samples were collected from 2,149 employees at Danderyd Hospital, of whom about 19 percent had antibodies against SARS-CoV-2. Blood samples have since then been collected every four months, and study participants have responded to questionnaires regarding long-term symptoms and their impact on the quality of life.

In the third follow-up in January 2021, the research team examined self-reported presence of long-term symptoms and their impact on work, social and home life for participants who had had mild COVID-19 at least eight months earlier. This group consisted of 323 healthcare workers (83 percent women, median age 43 years) and was compared with 1,072 healthcare workers (86 percent women, median age 47 years) who did not have COVID-19 throughout the study period.

The results show that 26 percent of those who had COVID-19 previously, compared to 9 percent in the control group, had at least one moderate to severe symptom that lasted more than two months and that 11 percent, compared to 2 percent in the control group, had a minimum of one symptom with negative impact on work, social or home life that lasted at least eight months. The most common long-term symptoms were loss of smell and taste, fatigue, and respiratory problems.

"We investigated the presence of long-term symptoms after mild COVID-19 in a relatively young and healthy group of working individuals, and we found that the predominant long-term symptoms are loss of smell and taste. Fatigue and respiratory problems are also more common among participants who have had COVID-19 but do not occur to the same extent," says Charlotte Thålin, specialist physician, Ph.D. and lead researcher for the COMMUNITY study at Danderyd Hospital and Karolinska Institutet. "However, we do not see an increased prevalence of cognitive symptoms such as brain fatigue, memory and concentration problems or physical disorders such as muscle and joint pain, heart palpitations or long-term fever."

"Despite the fact that the study participants had a mild COVID-19 infection, a relatively large proportion report long-term symptoms with an impact on quality of life. In light of this, we believe that young and healthy individuals, as well as other groups in society, should have great respect for the virus that seems to be able to significantly impair quality of life, even for a long time after the infection," says Sebastian Havervall, deputy chief physician at Danderyd Hospital and PhD student in the project at Karolinska Institutet.

The COMMUNITY study will now continue, with the next follow-up taking place in May when a large proportion of study participants are expected to be vaccinated. In addition to monitoring immunity and the occurrence of re-infection, several projects regarding post- COVID are planned.

"We will, among other things, be studying COVID-19-associated loss of smell and taste more closely, and investigate whether the immune system, including autoimmunity, plays a role in post-COVID," says Charlotte Thålin.

The biology of trauma: implications for treatment

During the past 20 years, the development of brain imaging techniques and new biochemical approaches has led to increased understanding of the biological effects of psychological trauma. New hypotheses have been generated about brain development and the roots of antisocial behavior. We now understand that psychological trauma disrupts homeostasis and can cause both short and long-term effects on many organs and systems of the body. Our expanding knowledge of the effects of trauma on the body has inspired new approaches to treating trauma survivors. Biologically informed therapy addresses the physiological effects of trauma, as well as cognitive distortions and maladaptive behaviors. The authors suggest that the most effective therapeutic innovation during the past 20 years for treating trauma survivors has been Eye Movement Desensitization and Reprocessing (EMDR), a therapeutic approach that focuses on resolving trauma using a combination of top-down (cognitive) and bottom-up (affect/body) processing.

Heroin’s Short-Term Effects on the Brain

The initial effects of heroin occur when the drug attaches to opioid receptors in the brain. This causes the euphoria of the initial high. It takes less than 20 minutes for the body to convert heroin to morphine and 6-MAM. That’s why most people say the initial high only lasts for between five and 15 minutes.

Morphine and 6-MAM stay in the brain for longer periods of time. These drugs continue to attach to opioid receptors for several hours. They likely cause prolonged effects that are milder than the initial high caused by heroin, according to a 2013 study published in the British Journal of Pharmacology.

Why Heroin Causes Pleasure & Pain Relief

When the body feels pleasure, such as when you hug a loved one, a small amount of endorphins attach to the brain’s opioid receptors. But heroin overwhelms the receptors, causing a large surge in happiness. That’s why many people say using heroin feels like extreme happiness or relaxation.

Opioid receptors affect more than happiness. Heroin can temporarily relieve feelings of depression or anxiety. The drug can also relieve pain the same way that prescription opioids relieve pain. High doses of opioids attach to opioid receptors, which prevents the brain from making you feel any type of pain.

The immediate positives associated with heroin aren’t worth the risks. Opioid receptors control important life functions, and heroin disrupts these processes. When the brain is flooded with heroin, opioid receptors in the brain can no longer tell the body how to function properly.

How Heroin Can Cause Brain Damage

The most common cause of immediate brain damage from heroin use occurs when the drug slows breathing to a dangerously low rate, according to the National Institute on Drug Abuse.

Heroin use can prevent the brain from receiving enough oxygen. Without oxygen, brain cells die. If enough brain cells die, the person dies. Most people who lose their life to heroin overdoses die because they stopped breathing.

People can survive heroin overdoses. The amount of brain damage caused by the overdose depends on how long they were without oxygen. Some people are able to fully recover because they weren’t without oxygen for enough time for brain cells to die.

But people may lose enough brain cells to severely change how their brain works. These people may need life support or assistance from caregivers for the rest of their lives.

What's Next…

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Marijuana smoke is harmful to your respiratory system, and vaping reduces the toxins that are found in smoke by up to 95%.

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If you want to experiment with CBD (which is one of the most beneficial compounds in marijuana), go to our list of recommended CBD oils.

Post last updated on: February 15, 2021

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