Master interaction table: Substances to avoid or use with caution
Always tell your GP and pharmacist about every prescription medicine, over-the-counter remedy, herbal supplement, and recreational substance you take:
| Substance Class | Common UK Examples | Risk Level | Clinical Mechanism & Risks |
|---|---|---|---|
| Opioids (Weak & Strong) | Codeine, co-codamol, tramadol, morphine, oxycodone, fentanyl, buprenorphine, methadone | SEVERE / HIGH RISK | Synergistic respiratory depression; severe sedation; loss of consciousness; fatal overdose. Avoid unless specifically co-prescribed under close specialist supervision. |
| Alcohol | Beer, wine, cider, spirits | HIGH RISK | Enhanced CNS depression, extreme drowsiness, loss of coordination, falls, memory blackouts, and impaired breathing. |
| Benzodiazepines & Z-Drugs | Diazepam, lorazepam, temazepam, clonazepam, zopiclone, zolpidem | HIGH RISK | Profound additive sedation, daytime somnolence, confusion, ataxia, and respiratory suppression. |
| Sedating Antidepressants | Amitriptyline, nortriptyline, mirtazapine, trazodone | MODERATE | Increased dizziness, unsteadiness, dry mouth, constipation, and heavy morning hangover effects. |
| ACE Inhibitors | Ramipril, lisinopril, enalapril, perindopril | MODERATE | Potential additive risk of angioedema (severe allergic swelling of the face, lips, tongue, or throat). |
| Sedating Antihistamines | Promethazine, chlorphenamine (Piriton), diphenhydramine (Nytol) | MODERATE | Severe drowsiness, slowed reaction times, impaired driving ability, and urinary retention. |
| Simple Analgesics & NSAIDs | Paracetamol, ibuprofen, naproxen | LOW / NO INTERACTION | Generally safe to combine when clinically indicated for musculoskeletal or inflammatory pain. |
1. The critical opioid combination: MHRA safety alerts
The co-prescription or co-ingestion of Pregabalin with opioid analgesics represents one of the most hazardous drug interactions in modern medicine. The UK MHRA has issued multiple urgent safety notices highlighting this danger.
Why this interaction is so dangerous:
- Synergistic effect: Opioids depress the respiratory centre in the brainstem. Pregabalin independently dampens brainstem firing. When combined, their effect is not just additive (1 + 1 = 2); it is synergistic (1 + 1 = 4).
- Blunted hypercapnic drive: Under normal conditions, if carbon dioxide builds up in your blood while asleep, your brain forces you to wake up and take deep breaths. The opioid-gabapentinoid combination blunts this survival reflex, leading to unobserved respiratory arrest during sleep.
Read our in-depth clinical guide on Pregabalin and opioids.
2. Pregabalin and alcohol
Alcohol is a central nervous system depressant that enhances GABA-mediated inhibition. Taking Pregabalin and drinking alcohol together can cause sudden, overwhelming drowsiness, profound loss of balance, slurred speech, and impaired judgment—even with modest amounts of alcohol.
Under UK law, driving with drugs in your system when impaired carries severe criminal penalties. Alcohol magnifies Pregabalin impairment exponentially. Read our dedicated guide on Pregabalin and alcohol.
3. Benzodiazepines and sleeping tablets
Medications prescribed for short-term anxiety or insomnia—such as diazepam (Valium), lorazepam, temazepam, and "Z-drugs" like zopiclone—also target inhibitory central pathways. Co-prescribing requires conservative starting doses and explicit warning regarding fall risks, daytime confusion, and impaired reaction times.
4. ACE inhibitors and angioedema risk
Angiotensin-converting enzyme (ACE) inhibitors (such as ramipril, lisinopril, and enalapril) are widely prescribed across the UK for hypertension and heart disease. Both ACE inhibitors and Pregabalin can independently cause angioedema (allergic fluid swelling of facial and pharyngeal tissues).
While co-administration is common in general practice, patients taking both must be educated to recognize early swelling of the lips, tongue, or throat and seek immediate emergency care (999) if swelling occurs. Read our serious side effects guide.
5. Over-the-counter medicines and herbal supplements
Do not assume that over-the-counter remedies bought in supermarkets or pharmacies are automatically safe with Pregabalin:
- Over-the-counter sleep aids: Products containing diphenhydramine (such as Nytol) or promethazine cause heavy additive sedation.
- Cough and cold remedies: Night-time cold syrups often contain sedating antihistamines, alcohol, or dextromethorphan, which can compound drowsiness.
- Herbal remedies: Supplements like Valerian root, St John’s Wort, and 5-HTP can increase sedation or mood instability. Always check with your pharmacist before taking herbal products.
Questions to ask your community pharmacist
- Are all my current repeat prescriptions safe to take alongside Pregabalin?
- Which over-the-counter painkillers or cold tablets can I safely take if I develop a headache or flu?
- Do any of my medications need to be taken at different times of the day to avoid severe tiredness?
- What should I do if a dentist or hospital doctor wants to prescribe a new medicine while I am on Pregabalin?