What happens when you take diphenhydramine with valerian?
Diphenhydramine is the first-generation antihistamine in Benadryl, ZzzQuil, Tylenol PM, Advil PM, and most over-the-counter 'PM' sleep aids. It produces sedation by blocking H1 histamine receptors in the brain and adds anticholinergic side effects (dry mouth, blurred vision, urinary retention, confusion) from its parallel muscarinic blockade.
Valerian (Valeriana officinalis) is a perennial flowering plant whose root is one of the most widely used herbal sleep aids in the United States and Europe. Its mechanism is not fully resolved, but valerenic acid and other constituents appear to modulate GABA-A receptors (similar in target to benzodiazepines but much weaker), inhibit GABA breakdown, and bind adenosine A1 receptors. The net effect is mild sedation and anxiolysis.
Combined, the two compounds produce additive central nervous system depression. Drugs.com Professional classifies the interaction as moderate and notes that 'sedation and impairment of attention, judgment, thinking, and psychomotor skills may increase.' For most healthy adults the consequence is heavier, longer-lasting drowsiness; for older adults or anyone with respiratory compromise (sleep apnea, COPD, heart failure), the additive depression can be clinically significant.
Why is this important?
The risk is not exotic toxicity but everyday safety. Excess sedation translates directly into:
- Next-day driving impairment. Diphenhydramine alone produces driving impairment comparable to a blood alcohol level of 0.05 to 0.10 percent for 8 to 12 hours after a 50 mg dose. Valerian deepens and extends this.
- Falls and fractures, especially when getting up at night. This is the dominant injury concern in adults over 65.
- Cognitive fog - diphenhydramine's anticholinergic effect impairs short-term memory and executive function. Adding a GABAergic agent on top blunts cognition further.
- Respiratory depression in vulnerable patients (sleep apnea, COPD, opioid users, elderly). Neither agent is a strong respiratory depressant alone, but the combination plus a third agent (alcohol, opioid, benzodiazepine) is dangerous.
The American Geriatrics Society Beers Criteria recommend avoiding diphenhydramine entirely for sleep in adults 65 and older because of anticholinergic burden, fall risk, and association with cognitive decline and dementia. Adding valerian to diphenhydramine in an older adult compounds the very risks the Beers Criteria are designed to prevent.
A subtler concern is sleep quality. Diphenhydramine suppresses REM sleep, the phase associated with memory consolidation and emotional processing. Valerian has a more neutral REM profile. Stacking them gives you more total sleep time but worse sleep architecture, which can leave you feeling unrefreshed even after a long night.
What should you do?
For occasional sleeplessness, choose one agent at the lowest effective dose rather than stacking. Sensible options:
- If anxiety or muscle tension is keeping you awake, valerian (300 to 600 mg of root extract, 30 to 60 minutes before bed) can help. Skip diphenhydramine.
- If allergy symptoms are the problem, take a non-sedating second-generation antihistamine (cetirizine, loratadine, fexofenadine) during the day and skip the 'PM' product at bedtime.
- If you genuinely need a stronger short-term sleep aid, talk to a pharmacist or clinician about pairing one agent with sleep hygiene rather than stacking two over-the-counter sedatives.
If you must take both occasionally, take them only at bedtime, do not combine with alcohol, opioid pain medications, or benzodiazepines, and plan to spend at least 8 hours in bed. Do not drive or operate machinery the next morning if you feel groggy. Watch for paradoxical agitation in children and older adults; diphenhydramine can produce confusion, restlessness, and hallucinations rather than sedation in these populations.
For chronic insomnia, neither diphenhydramine nor valerian is a long-term solution. Tolerance develops within days to weeks. 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 (often standardized to 0.8% valerenic acid)
- 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
The bottom line
Diphenhydramine and valerian are both legitimate short-term sleep aids on their own, but combining them produces excess sedation and elevated risk of next-day impairment, falls, and cognitive fog. For most adults the safer plan is to use one agent at the lowest dose, address the root cause of poor sleep, and reserve over-the-counter sleep aids for occasional use rather than nightly routine. Adults 65 and older should avoid diphenhydramine entirely for sleep and use valerian or low-dose melatonin instead if a sleep aid is needed.