Diazepam Side Effects: What to Expect and When to Call Your Doctor

Starting diazepam (Valium) for anxiety, muscle spasms or seizures can feel like a relief — but like every prescription medicine, it can cause side effects. Knowing what is normal, what is manageable, and what needs urgent medical attention helps you use it safely. This guide explains the common side effects of diazepam in plain English for UK patients.

Important: diazepam is a prescription-only medicine in the UK. Never start, stop or adjust it without your GP or pharmacist. If you need a legitimate supply with a valid prescription, you can order through our registered pharmacy shop.

Common Side Effects of Diazepam

Most people tolerate diazepam well, especially for short courses. The most frequently reported effects include drowsiness or sleepiness, dizziness, feeling unsteady, blurred vision, dry mouth, constipation, nausea, headache and a general feeling of tiredness or weakness. These often ease within a few days as your body adjusts.

Drowsiness is the big one: avoid driving, operating machinery or drinking alcohol while taking diazepam. Alcohol intensifies sedation and breathing risks — the combination should be avoided completely. If sleepiness interferes with work or daily life, speak to your prescriber rather than skipping doses on your own.

Mood and Memory Effects

Diazepam works by calming activity in the brain, which can also affect mood and memory. Some people notice forgetfulness (especially for events after taking a dose), confusion, slower reactions, low mood or unusual vivid dreams. Elderly patients are more sensitive to these effects and usually need extra caution and review.

Rarely, people experience the opposite of calm — restlessness, agitation, irritability or aggression. These paradoxical reactions are uncommon but should be reported to your GP promptly. Our complete safety guide to buying and using diazepam explains how proper prescribing reduces these risks.

Dependence, Tolerance and Withdrawal

With continued use, the body can become dependent on diazepam — meaning stopping suddenly causes withdrawal symptoms such as rebound anxiety, insomnia, sweating, tremor, nausea and, rarely, seizures. This is why UK guidelines recommend the lowest effective dose for the shortest necessary time, with regular prescriber reviews.

Never stop diazepam abruptly after more than a couple of weeks of use. Your GP will arrange a gradual taper plan. Wondering about strengths? Read our comparison of diazepam 5mg vs 10mg to understand how prescribers choose doses — but the decision itself always belongs to your doctor.

Serious Side Effects: When to Get Urgent Help

Seek urgent medical attention (NHS 111, or 999 in an emergency) if you or someone else experiences very slow or difficult breathing, extreme sleepiness or inability to wake up, severe confusion, fainting, yellowing of the skin or eyes, a severe skin rash, or signs of an allergic reaction such as swelling of the face, lips or throat.

Overdose signs include severe drowsiness, slurred speech, loss of coordination and loss of consciousness. Keep diazepam out of reach of children at all times, and store it in its original packaging so the label and expiry date stay visible.

Interactions With Other Medicines

Diazepam interacts with many common medicines: strong painkillers (especially opioids), sleeping tablets, certain antidepressants and antipsychotics, antihistamines that cause drowsiness, and some epilepsy medicines. Always tell your GP and pharmacist everything you take — including over-the-counter remedies, herbal products and supplements.

Grapefruit juice can raise diazepam levels in the blood and is best avoided. If you take other regular medicines, a pharmacist medication review once or twice a year is good practice. You can contact our pharmacy team with general questions about your prescription medicines.

Tips for Using Diazepam Safely

Take it exactly as prescribed, at the same times each day. Ask your prescriber how long diazepam takes to work so you know what to expect instead of taking extra doses. Attend review appointments, keep a note of any side effects to discuss, and never share your tablets with anyone else — what is safe for you may be dangerous for them.

Check our frequently asked questions for more on ordering, delivery and prescription requirements in the UK.

Frequently Asked Questions

How long do diazepam side effects last?

Mild effects like drowsiness or dizziness usually settle within a few days of starting or after a dose adjustment. Tell your GP if they persist beyond a week or worsen.

Can I drive while taking diazepam?

Usually not at first. UK drug-driving law covers diazepam, and drowsiness makes driving unsafe. Ask your prescriber when — if ever during treatment — driving is safe for you.

Is it safe to drink alcohol with diazepam?

No. Alcohol increases sedation, breathing problems and overdose risk. Avoid alcohol completely while taking diazepam.

What should I do if I miss a dose?

Take it when you remember unless it is nearly time for the next dose — never double up. Ask your pharmacist if you are unsure.

Disclaimer: this article is for general information only and is not medical advice. Always follow your prescriber’s instructions and consult your GP or pharmacist about side effects or concerns.