A total of 141 runners needed treatment in what fire service officials described as "an emergency with mass casualties."
Eighteen ambulances were deployed as part of an emergency rescue response.
The 21.0975-kilometer race had attracted 11,215 entries, but 8,402 were at the start and 8,056 finished, organizers said.
The men's race was won by 2012 Olympic marathon champion Stephen Kiprotich of Uganda in 1 hour 4 minutes 11 seconds, ahead of Kenya's Geoffrey Rono (1:04:43) and Ethiopia's Haimonet Mateb Muluneh (1:05:02).
Melat Kejeta of Germany won the women's race in 1:11:29 ahead of Gladys Jeptepkeny of Kenya (1:13:22) and Tabitha Gichia Wambui of Kenya (1:15:33).
In Frankfurt, U.S. triathlete Sarah True needed medical treatment after collapsing while leading shortly before the end of the Ironman European Championship held in temperatures close to 40 degrees Celsius.
Medical attendants carried 37-year-old True from the course after she collapsed some 1,000 meters from the end of the marathon stretch of the swimming, cycling and running event.
"I can't remember the last kilometers," she said after recovering.
Fellow American Skye Moench won the title, while Germany's Jan Frodeno won the men's European title for a third time.
