编写一个Python函数，接受一个整数列表作为参数，并返回列表中所有元素的乘积。

[1, 2, 3, 4, 5]
```python
def multiply(numbers):
    result = 1
    for n in numbers:
        result *= n
    return result

numbers = [1, 2, 3, 4, 5]
print(multiply(numbers)) # Output: 120
```