"Does my BMI look big on this?" : opioids and weight gain.

Dr Kirstie Anderson from the Regional Sleep Service, Newcastle, writes about the often misunderstood problem of opioids and weight gain in pain patients.

When I teach medical students, I suggest that, before they prescribe any drug, they check some basics. Does the patient sleep well or badly, are they under or overweight, happy or sad? For many long-term conditions, fewer than 50% of patients take their drugs as prescribed. This is often due to unpleasant side effects, so we should try and personalise our prescribing whenever possible. Most of us don't like feeling dizzy, nauseous or groggy and our patients are no different. However many patients don't fully understand the potential side effects of medication and weight gain in particular seems poorly understood.

I see many patients with chronic low back pain and obstructive sleep apnoea (OSA); lots have both but most are only aware of the first. OSA is often a dawning diagnosis. Tired all the time usually gets a full blood count, a depression screen and vitamin D replacement before the penny drops. Even then, it is usually only because the bed partner describes snoring that rattles the windows and long pauses in breathing. Some risk factors for OSA can't easily be changed, for example, getting old and being male. NICE have yet to approve a cure for ageing and men's anatomy makes them snore more. However, the biggest risk factor is being too big: 80% of those with OSA are obese. The obesity epidemic is also cited as contributing to increasing back and joint pain, alongside sedentary lifestyles.

Drugs that cause weight gain should, therefore, be prescribed with caution. Pain relief for low back pain that causes weight gain seems particularly unhelpful. There has been an 800% increase in prescriptions for pregabalin and gabapentin in the last 10 years, partly in response to concerns about opioids. The latest national prescribing data shows that many patients simply end up both on strong opioids and a gabapentinoid. This is despite limited evidence for benefit and increasing recognition of significant side effects. A recent meta-analysis of pregabalin demonstrated a number needed to harm of only 7. Pregabalin and gabapentin typically cause a dose-dependent weight gain within the first 3 months of prescribing. Up to a 14% increase in BMI is seen in those on 300mg bd of pregabalin.

Do opioids make you fat? Well, they may do, based on recent work from the Biobank cohort, one of the world's largest cohort studies, recruiting nearly half a million UK participants in 2007. Our own research in Newcastle studied 133,401 taking prescribed medication and showed that those on opioids had double the risk of increased weight, worse cardiometabolic health, decreased physical activity and also worse sleep. This was compared to people taking a wide range of other commonly prescribed medications. The reasons seem likely to be multifactorial. Sedative drugs may decrease physical activity, they certainly cause or worsen sleep apnoea and this remains largely undiagnosed in the population. Whether they have a direct effect on appetite remains debated.

So, does it help to let people know about potential weight gain? The short answer seems to be yes - most of us don't like weight gain as a side effect. It often surprises me that opioid discussions with patients around addiction, lack of benefit and increased risk carry less weight than weight. Telling someone that they are likely to be slimmer off the drugs than on them can motivate change. In terms of routine practice, this does mean that weight needs to be a standard measure across outpatient clinics, and that we need to support weight loss as part of pain management. GPs seem better at this than some of my hospital colleagues.

It is interesting that a completely standard discussion within the diabetic and hypertension clinics rarely seems to be touched upon in rheumatology or pain clinics in our region. Shying away from these sometimes difficult conversations can be tempting. However quick fixes using the latest, expensively packaged poppy seeds are what got us - and our chronic pain patients - into this mess in the first place.

Tadesse MA, Lamessa MS, and Hussien NT. Self-Reported Adverse Drug Reactions, Medication Adherence, and Clinical Outcomes among Major Depressive Disorder Patients in Ethiopia: A Prospective Hospital Based Study. Psychiatry J. 2017; 2017: 5812817.

Shanthanna H, Gilron I, Rajarathinam M, et al. Benefits and safety of gabapentinoids in chronic low back pain: A systematic review and meta-analysis of randomized controlled trials. PLoS Med. 2017 Aug 15;14(8):e1002369.

Cassidy S, Trenell M, Anderson KN. The cardio-metabolic impact of taking commonly prescribed analgesic drugs in 133,401 UK Biobank participants. PLoS ONE 12(12): e0187982.