The findings are based on anonymous interviews with patients visiting an inner city hospital emergency care department in South West England during a typical week.
The treating doctor was also asked to assess whether the patient's need for treatment was indirectly or directly related to illicit drug use.
In all, 1070 patients sought emergency care during the week, 801 of whom were interviewed.
Over a third (36%) admitted to illicit drug use at some time during their lives, and 16% said they had used illegal drugs in the previous month. Almost one in 10 said they had "used" within the previous 24 hours.
The treating doctor judged that the reason for seeking emergency care was directly or indirectly related to their drug use in just under 7% of cases.
Twenty-three patients had to be admitted to hospital, representing just under 3% of all those interviewed. The most common reasons for admission included self harm, skin infections, chest pain and deep vein thrombosis.
The authors say the findings of lifetime illegal drug use more or less match those reported in the British Crime Survey. But the figures for drug use within the preceding month are nearly three times as high. This suggests that recent or current drug use greatly increases the risk of requiring emergency care, they say.
"...with annual Emergency Department attendances currently exceeding 14 million in England alone, it is possible that illegal drugs contribute directly or indirectly to 1 million ED attendances and 40,000 acute hospital admissions in England each year," they conclude.