Up to a third of people prescribed metformin – the most commonly prescribed drug for treating type 2 diabetes – are not taking the drug, our latest research shows. Not only is this putting a large number of people with diabetes at increased risk of serious complications, it is also a huge waste of money.
If people with diabetes don’t control their blood sugar, it eventually leads to complications including blindness, kidney failure and heart disease. Metformin helps to lower blood sugar levels by lowering the amount of sugar made by the liver. The drug also increases the sensitivity of muscle cells to insulin.
However, metformin isn’t the only drug that people with type 2 diabetes are able to use. There is a wide range of drugs that can be used to improve blood sugar regulation. Some are taken in pill form, others are injected. Some can be used once weekly, whereas others must be taken several times a day. All of these things can influence how likely a person is to take their medicine as prescribed.
Each drug has a unique way of working and also comes with a unique set of side effects. Despite this abundance of choice, it was not previously clear which drugs people with diabetes find easiest to take and which are more likely to be left in the medicine cabinet.
For our review, we looked for studies comparing medication use in people with type 2 diabetes. We found 48 relevant studies describing medication use in a total of 1.7m people with diabetes.
Lots to choose from
Our analysis of the combined data (a meta-analysis) found that around 30% of metformin doses never get taken. For other medication types the proportion of missed doses was much lower, with 23% of sulfonylureas (such as gliclazide) and 20% of pioglitazone going untaken. DPP4 inhibitors (gliptins), one of the newer medication classes, have the highest rates of use, with only 10-20% of medication doses not taken.
When comparing injectable drugs, we found that people are twice as likely to stop taking GLP1 receptor agonists (such as exenatide), compared with insulin.
We were surprised to find such large differences in the number of missed doses between the different classes of drugs. We were also surprised to find that the use of metformin was so low.
Metformin can cause diarrhoea and flatulence, which may be part of the reason so many people stop taking it, but it is a worrying result nonetheless. Also, to get a good effect from metformin it may have to be taken two or three times a day. The good news is that there are some drugs that people with diabetes find easier to take.
Gliptins (such as sitaglitpin) have very few side effects and are usually only taken once a day, so it’s understandable why fewer doses of this drug class are missed.
Pioglitazone is one of the older diabetes drugs, and its use has fallen out of favour since its sister drug rosiglitazone was found to cause heart disease and was withdrawn from the market. Pioglitazone has since been confirmed to be safe but is still less commonly prescribed. It was very interesting to see that this older drug – out of favour with doctors – was one of the most well tolerated by patients.
Although metformin is known to have some advantages over other diabetes drugs, particularly in protecting against heart disease, these effects can’t be achieved if people aren’t taking it. As there are lots of treatment options for type 2 diabetes, switching to a different medication – one that is easier to take – is a much better option than taking no drug at all.
Andrew McGovern previously received research funding from AstraZeneca and Eli Lilly.