Handouts · Medications
Antihistamines & Anticholinergics
Includes diphenhydramine (Benadryl), hydroxyzine (Vistaril), and benztropine (Cogentin). Used for anxiety, sleep, itching, or to ease medication-related muscle stiffness.
What These Are
These medicines block histamine and/or acetylcholine in the body and brain.
• Hydroxyzine (Vistaril) and diphenhydramine (Benadryl) are antihistamines used for anxiety, sleep, or itching.
• Benztropine (Cogentin) is an anticholinergic used to ease muscle stiffness or tremor caused by antipsychotic medicines.
How to Take It
Take with or without food. The antihistamines are sedating — if used for sleep or anxiety, they are often taken at night or as needed.
Benztropine is usually taken on a set schedule. Do not exceed the prescribed dose.
Important Cautions
There is no “black box” warning, but a few cautions are important:
• Best avoided as a regular medicine in older adults — they raise the risk of confusion, falls, and memory problems.
• Hydroxyzine can affect heart rhythm (QT) at higher doses — tell us about any heart-rhythm history.
• Diphenhydramine is dangerous in overdose.
Common (Usually Mild) Side Effects
- Drowsiness.
- Dry mouth, dry eyes.
- Blurred vision.
- Constipation, trouble urinating.
Serious — Call Us or Seek Care
- Confusion, agitation, or hallucinations — especially in older adults.
- Cannot urinate, or severe eye pain/blurred vision (can worsen certain glaucoma).
- Fast or irregular heartbeat, or fainting.
- Overheating — these reduce sweating, so be careful in hot weather or hard exercise.
Alcohol & Interactions
Avoid alcohol — it adds strongly to the drowsiness.
Tell us about other sedatives and about any other anticholinergic medicines — the effects stack up and raise the risk of confusion.
Monitoring
No routine blood tests are needed.
In older adults, we keep an eye on thinking, balance, and fall risk, and try to limit long-term use. An EKG may be checked before higher-dose hydroxyzine if you have heart-rhythm risks.