Lantus, the reference insulin glargine used for the treatment of diabetes, lost its patent protection in 2014, opening the market to biosimilar competitors.First, to analyze the adoption rates of insulin glargine biosimilars in primary care in England and estimate the savings realized and missed, since an insulin glargine biosimilar was first used, and second, to assess potential variations in adoption rates across Clinical Commissioning Groups (CCGs).Data sets capturing information on all insulin glargine items prescribed by all general practitioners up to December 2018 were used. Total costs of insulin glargine and uptake rates of biosimilars were calculated. The real-world budget impact was estimated assuming the cost of reference insulin glargine for all items and comparing the total costs in this scenario with the total costs in the real world. The missed savings were estimated assuming the cost of biosimilars for all insulin glargine items. Choropleth maps were generated to assess potential variations in uptake across CCGs.Insulin glargine biosimilars generated savings of £900,000 between October 2015 (time of first prescription) and December 2018. The missed savings amounted to £25.6 million in this period, indicating that only 3.42% of the potential savings were achieved. The analyses demonstrated a large level of variation in the uptake of insulin glargine biosimilars across CCGs, with market shares ranging from 0 to 53.3% (December 2018).These results may encourage decision makers in England to promote the use of best-value treatments in primary care and to reevaluate variation across CCGs.