What happens when you take diphenhydramine with valerian?
Diphenhydramine is the first-generation antihistamine in Benadryl, ZzzQuil, Tylenol PM, and most over-the-counter "PM" sleep aids. Valerian (Valeriana officinalis) is one of the most widely used herbal sleep aids. Both calm the brain, but through different routes, so taking them together stacks two sedatives at once.
- Diphenhydramine blocks histamine. It blocks H1 histamine receptors in the brain to produce drowsiness, and also blocks muscarinic receptors, which adds anticholinergic effects such as dry mouth, blurred vision, urinary retention, and confusion.
- Valerian nudges the GABA system. Its valerenic acid and related constituents appear to modulate GABA-A receptors (a much weaker version of how benzodiazepines work), slow GABA breakdown, and bind adenosine A1 receptors. The net effect is mild sedation and a calming, anxiety-reducing action.
- The two effects add together. With one drug damping the brain through histamine and the other through GABA, the sedation combines. Drugs.com Professional classifies this as a moderate interaction and notes that sedation and impairment of attention, judgment, thinking, and psychomotor skills may increase.
For most healthy adults the practical result is heavier, longer-lasting drowsiness. For older adults or anyone with breathing problems (sleep apnea, COPD, heart failure), the added depression matters more.
Why is this important?
The concern here is not exotic toxicity, it is everyday safety. Stacking two sedatives mostly translates into excess drowsiness and slower reactions, and that shows up in a few predictable ways:
- Next-day impairment. Diphenhydramine can leave people groggy and slow to react well into the following morning. Valerian deepens and lengthens that effect, so driving or other demanding tasks the next day can be riskier than expected.
- Falls and fractures. Excess sedation raises the chance of a fall, especially when getting up at night. This is the dominant injury concern in adults over 65.
- Cognitive fog. Diphenhydramine's anticholinergic action blunts short-term memory and clear thinking; adding a sedating herb on top can make that worse.
- Breathing in vulnerable people. Neither agent is a strong respiratory depressant on its own, but the combination can matter in people with sleep apnea, COPD, or heart failure, and especially if alcohol, opioids, or benzodiazepines are also in the mix.
The American Geriatrics Society Beers Criteria recommend avoiding diphenhydramine altogether for sleep in adults 65 and older, because of anticholinergic burden, fall risk, and links to cognitive decline. Adding valerian on top compounds the very risks that guidance is meant to prevent.
A subtler point is sleep quality: diphenhydramine suppresses REM sleep, the phase tied to memory and emotional processing. Stacking sedatives can buy more total sleep time while leaving sleep less restorative, so you may still wake unrefreshed.
What should you do?
The simplest safe approach is to pick one agent rather than stacking two, use it at the lowest amount that works, and time it sensibly. Here is a practical schedule.
Before any change:
- List everything you already take for sleep, allergies, or pain, including "PM" products and herbal blends, so you can spot diphenhydramine and valerian hiding under brand names.
- Review the plan with your doctor or pharmacist, especially if you are over 65 or have sleep apnea, COPD, or heart failure.
On a given night / every day:
- If anxiety or restlessness is keeping you awake, consider valerian alone, taken a half hour or so before bed, and skip diphenhydramine.
- If allergy symptoms are the real problem, use a non-drowsy second-generation antihistamine (such as cetirizine, loratadine, or fexofenadine) during the day and skip the bedtime "PM" product.
- If you do use either agent, take it only at bedtime, keep the amount low, and avoid alcohol, opioid pain medicines, and benzodiazepines the same night.
- Plan to spend a full night in bed so the sedation has time to wear off.
After taking it:
- Do not drive or operate machinery the next morning if you feel groggy.
- Watch for paradoxical agitation, restlessness, confusion, or hallucinations, which diphenhydramine can cause in children and older adults instead of sleepiness.
- For ongoing insomnia, remember neither agent is a long-term fix; cognitive behavioral therapy for insomnia (CBT-I) is the recommended first-line treatment.
Which specific products are affected?
Diphenhydramine-containing products to watch for:
- Benadryl Allergy, Benadryl Allergy Plus Cold
- ZzzQuil, Vicks NyQuil
- Tylenol PM, Advil PM, Aleve PM
- Unisom SleepGels (note: Unisom SleepTabs contain doxylamine, a related antihistamine with similar concerns)
- Sominex, Nytol
- Most store-brand "PM" pain relievers and OTC sleep aids
Valerian-containing products:
- Single-ingredient valerian root capsules
- Valerian tinctures, teas, and liquid extracts
- Combination "sleep" or "calm" herbal blends with hops, passionflower, chamomile, lemon balm, or skullcap
- Multi-ingredient supplements pairing valerian with melatonin, magnesium, GABA, or L-theanine
Read labels on any OTC "PM" product: diphenhydramine is the default sedating ingredient and is easy to take inadvertently alongside an herbal sleep blend.
The science behind it
The clearest documentation of this pairing comes from clinical interaction references. Drugs.com Professional lists diphenhydramine with valerian root as a moderate interaction, on the basis that both are central nervous system depressants and their sedative and psychomotor effects are additive. This is the same additive-sedation logic applied to any two CNS depressants taken together.
The underlying additivity has also been examined in animal pharmacology. An isobolographic study in mice (Ugalde and colleagues, 2005) tested a Valeriana hydroalcoholic extract combined with several CNS depressant drugs, including diphenhydramine, and found the sedative interaction was additive rather than synergistic, meaning the effects sum but do not multiply. As an animal (mouse) study it does not by itself prove an effect in people, but it supports treating the combination as a real and predictable increase in drowsiness, not an outsized or unpredictable danger. Direct human trials of this specific pair are lacking, so the practical guidance rests on the shared mechanism and the moderate rating in clinical references.
Frequently Asked Questions
Is it dangerous to take Benadryl and valerian together once?
For a healthy adult, an occasional single combined dose at bedtime is most likely to cause extra grogginess rather than serious harm. The main risks are next-morning impairment and falling if you get up during the night, so do not drive until the drowsiness has fully worn off.
Why is this riskier for older adults?
Diphenhydramine is on the Beers Criteria list of medicines to avoid in people 65 and older because of its anticholinergic effects, fall risk, and links to cognitive decline. Adding a second sedative such as valerian magnifies those concerns.
Can I take valerian during the day and diphenhydramine at night?
Separating them in time reduces the overlap, but both can linger, so some sedative overlap may still occur. If you need both, it is safer to discuss the plan with a pharmacist rather than self-managing the timing.
What about alcohol with this combination?
Avoid it. Alcohol is itself a CNS depressant, so adding it to diphenhydramine and valerian increases sedation, impairment, and the risk of slowed breathing in vulnerable people.
Which is the better single choice for sleep?
It depends on the cause. For occasional anxiety-related sleeplessness, valerian alone is a reasonable option. For allergy-driven sleep trouble, a non-drowsy daytime antihistamine plus good sleep habits is usually better than a bedtime sedating antihistamine.
What should I use for long-term insomnia?
Neither of these is a long-term solution; tolerance develops quickly. Cognitive behavioral therapy for insomnia (CBT-I) is the recommended first-line treatment and works better over time.
Key takeaways
- Diphenhydramine and valerian both sedate the brain, so taking them together adds up to more drowsiness, slower reactions, and a higher fall risk.
- The interaction is rated moderate and is additive, not an extreme or unpredictable danger, but it still matters for safety.
- Prefer one agent at the lowest effective amount, avoid alcohol and other sedatives, and do not drive until you know how you are affected.
- Adults 65 and older should avoid diphenhydramine for sleep entirely.
- For ongoing insomnia, CBT-I is the recommended first-line approach; review your sleep-aid plan with your doctor or pharmacist.