The giant jellyfish, also known as the Nomura's jellyfish or the Nemopilema nomurai, is not typically deadly to humans, but it can cause moderate pain and irritation. Its sting is not known to be fatal. However, there are some other species of jellyfish, such as the box jellyfish and the Irukandji jellyfish, whose stings can be deadly to humans.

The venom of these jellyfish contains a variety of toxins that can cause a range of symptoms, including pain, nausea, vomiting, diarrhea, muscle cramps, and difficulty breathing. In severe cases, jellyfish stings can lead to paralysis, heart failure, and death. The potency of the venom varies between different species of jellyfish and can also depend on factors such as the size of the jellyfish, the amount of venom injected, and the individual's sensitivity to the venom.